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1 .frB Agriculture 



Canada 

Research Direction generale 
Branch de la recherche 

Technical Bulletin 1990-5E 



A manual on guidelines for 
the control of arboviral 
encephalitides in Canada 



B .J. j Agriculture 



Canada 



DEC 1 3 1990 

Library / Bibliotheque, Ottawa K1A 0C5 



630.72 
C759 

c qp-5* 
C 2> 




•• 



Canada 



Digitized by the Internet Archive 
in 2013 



http://archive.org/details/manualonguidelin19905cana 



A manual on guidelines for 
the control of arbo viral 
encephalitides in Canada 



Submitted by 

The Canada Biting Fly Centre 
Department of Entomology 
The University of Manitoba 

Technical Bulletin 1990-5E 



Research Branch 
Agriculture Canada 
1990 



Copies of this publication are available from 

Peter G. Mason 

Secretary 

Expert Committee of Insect Pests of Animals 

Research Branch, Agriculture Canada 

107 Science Crescent 

Saskatoon. Saskatchewan 

S7N 0X2 

Produced bv Research Program Service 

s Minister of Supplv and Services Canada 1990 

Cat. No. A54-8/1990-5E 

ISBN 0-662-18197-2 

Contract DSS No. OSF85-00073 



Cover illustration 

The dots on the map represent 
Agriculture Canada research 
establishments. 



TABLE OF CONTENTS 

PART I 

PAGE 

1. INTRODUCTION 3 

2. DISEASES 8 

a. Western Equine Encephalitis 8 

i. History 8 

ii. Nature of Disease 9 

iii. Clinical Aspects in Human Infections 10 

iv. Epidemiology 13 

b. St. Louis Encephalitis 23 

i. History 23 

ii. Nature of Disease 24 

iii. Clinical Aspects in Human Infections 25 

iv. Epidemiology 25 

c. Eastern Equine Encephalitis 26 

i. History 26 

ii. Clinical Aspects 27 

iii. Epidemiology 28 

3. VECTORS 29 

a. Known and Potential Vectors of Western Equine 
Encephalitis 29 

i. Survey of Virus Isolations 29 

ii. Virus Amplification 31 

iii. Transmission 31 

iv. Overwintering of Vectors 33 

b. Known and Potential Vectors of Eastern Equine 
Encephalitis 34 

c. Known and Potential Vectors of California 

Group Viruses 35 

d. Possible Overwintering of Viruses 37 

4. SURVEILLANCE 42 

a. Mosquito Populations 42 

i. Larval Surveys 42 

ii. Adult Surveys 42 

iii. Population Dynamics, Activity 45 

iv. Interpretation of Trap Data 47 

b. Virus Activity 49 

iii 



i. Mosquito Populations 49 

ii. Sentinel Flocks 50 

iii. Reservoirs, Indicators 51 

c. Criteria 52 

i. Mosquito Counts 52 

ii. Significance of Seroconversion 54 

iii. Weather Factors 54 

d. Provincial Surveillance 55 

i. Western Equine Encephalitis 55 

ii. St. Louis Encephalitis 60 

5. CRITERIA FOR CONTROL 61 

a. Western Equine Encephalitis 61 

b. St. Louis Encephalitis 68 

6. CONTROL OPTIONS 69 

a. Vector Suppression 69 

i. Non- Chemical 70 

ii. Use of Insecticides 71 

iii. Aerial Insecticide Application 77 

iv. Activity Periods of Vectors 80 

v. Honey Bee Activity 81 

b. Host Protection 83 

i. Suitable Clothing 83 

ii. Screening and Netting 83 

iii. Behaviour Modification 84 

iv. Topically Applied Repellents 85 

v. Repellent- impregnated Clothing 86 

vi. Personal Hygiene 87 

vii. Human Vaccination 87 

viii. Devices for Protection 87 

ix. Horse Vaccination 87 

x. Repellents for Horses 88 

xi. Smudges 88 

xii. Insecticides 98 

7. EMERGENCY VECTOR CONTROL 89 

a. Emergency Vector Control by Municipalities 89 

b. Value of Ground-Based Control 95 

c. Assessment of Repellents 96 

8. ENVIRONMENTAL MONITORING 101 



iv 



a. Spray Dispersal 101 

b. Effects on Wildlife 103 

c. Effects on Humans 105 
9. PUBLIC INFORMATION 117 

a. Information Program 117 

b. Media Option 120 

c. Resource Materials 121 

d. Specific Needs 124 

PART II 

1. SURVEILLANCE PROGRAM 127 

a. Protocols for Arbovirus Surveillance 127 

b. Resource Requirements for Surveillance 

Program 127 

c. Components for Surveillance 128 

i. Weather 128 

ii. Mosquito Monitoring 128 

iii. Virus Activity 130 

iv. Equine Cases 132 

v. Human Cases 133 

vi. Contributions and Activities of 

Other Jurisdictions 133 

d. Approach 133 

2. CONTINGENCY PLANNING FOR IMPLEMENTATION OF 
EMERGENCY VECTOR CONTROL 135 

a. General Approach to Aerial ULV Applications 135 

b. Resource Requirements 136 

c. Planning and Scheduling 141 

d. Legislation and Jurisdiction 142 

e. Procedural Guidelines 144 

f . Reporting Procedures 147 

v 



3. PUBLIC INFORMATION 149 

a. Implementation 149 

b. Maintenance Requirements 150 

c. Assessment 155 

PART III 

REFERENCES CITED 158 



APPENDIX 

I. INVENTORY OF CHEMICALS REGISTERED IN CANADA 

FOR MOSQUITO CONTROL AND AS REPELLENTS 193 

II. INVENTORY OF EQUIPMENT USED IN CANADA FOR 

MOSQUITO CONTROL 202 

III. SUPPLIERS OF REPELLENTS AND CHEMICALS 

REGISTERED FOR MOSQUITO CONTROL IN CANADA 207 

IV. ARBOVIRUS SURVEILLANCE PROGRAMS IN CANADA, 1980 215 



VI 



PART I 



1. INTRODUCTION 

Mosquito-borne virus outbreaks in Canada have typically been 
sporadic and unpredictable. Consequently, when there is an 
outbreak, communities are caught by surprise and may be poorly 
prepared for the public health emergency to follow. The Canada 
Biting Fly Centre was contracted to help synthesize available 
information on mosquito -borne arboviruses in Canada, and to 
provide officials with the emergency measures necessary during an 
outbreak. 

The contract was initiated by the Expert Committee of Insect 
Pests of Animals (Agriculture Canada) , and expertise was drawn 
from the membership of The Expert Committee on Insect Pests of 
Animals. Contributing members of that Committee and other 
collaborators are listed below, followed by their sections of 
responsibility: 
Dr. R.A. Brust - Dept. of Entomology, University of Manitoba, 

Winnipeg, Manitoba. R3T 2N2 . Part I. Sections 3a(i, ii, iii, 

iv) , 4a(iii, iv) , 4b(i, ii) , 4c(i,ii, iii), 6a(iv, v) , 7b. 
Dr. R.A. Costello - British Columbia Ministry of Agriculture and 

Fisheries, 1770 -57th Ave. , Surrey, British Columbia. V3S 

1Z4. Part I. Section 4a(i, ii) . 
Dr. R.A. Ellis - Prairie Pest Management, 207 Cullen Dr., 

Winnipeg, Manitoba. R3R 1P5 . Part I. Sections 6a(i, ii, 

iii), 6b, 7a, c, 9a, b, c, d; Part II. 2, 3; Appendices I, 

II, and III. 
Dr. M.M. Galloway, Director, Canada Biting Fly Centre, Dept. of 

Entomology, University of Manitoba, Winnipeg, Manitoba. R3T 

2N2. Part I. Sections 4d(i), 5a; Part II, la, b, c, d; 

Appendix IV. 
Dr. T.D. Galloway, Dept. of Entomology, University of Manitoba, 

Winnipeg, Manitoba. R3T 2N2 . Part I. Sections 2a(i, ii, iii, 

iv), 3b, c, d, 4b(iii), 4d(ii), 5b. 
Dr. W.L. Lockhart, Dept. of Fisheries and Oceans, Freshwater 

Institute, 501 University Crescent, Winnipeg, Manitoba. R3T 

2N6. Part I. Sections 8a, b, c. 
Dr. P.N. Nation, Head, Veterinary Pathology Branch, Alberta 

Agriculture, 6909 116 St., Edmonton, Alberta. T6H 4P2 . Part 

I. Section 2a(i), Alberta data in Table 2. 
Dr. H.J. Smith, Food Production and Inspection Branch, Health of 

Directorate, Animal Pathology Division, Box 1410, 13 College 

St., Sackville, New Brunswick. E0A 3C0. Part I. Sections 

2c(i, ii, iii) . 
Dr. G.A. Surgeoner, Dept. of Environmental Biology, University of 

Guelph, Guelph, Ontario. NIG 2W1. Part I. Sections 2b(i, ii, 

iii, iv). 

Funding for this project was provided through a contract 
from Agriculture Canada to The Canada Biting Fly Centre. 

The support and financial assistance provided by Dean J.I. 
Elliot and former Dean R.C. McGinnis of the Faculty of 
Agriculture, University of Manitoba, and the Office of Research 



Administration of the University of Manitoba are gratefully 
acknowledged. The assistance of Mr. R.M. Prentice, former Chair, 
and Dr. R. Trottier, Chair, of the Expert Committee of Insect 
Pests of Animals (Agriculture Canada) is also gratefully 
acknowledged . 



1. INTRODUCTION 

Au Canada, les foyers de virus transmis par les moustiques ont toujours 
ete sporadiques et imprevisibles. En consequence, lorsqu'un foyer se declare, 
les populations touchees sont prises au depourvu et sont souvent mal preparees 
a faire face a la situation d'urgence sanitaire qui en decoule. On a done 
retenu les services du Centre canadien sur les insectes piqueurs pour 
participer a la synthese de 1' information disponible sur les arbovirus 
transmis par les moustiques au Canada et pour indiquer aux fonctionnaires les 
mesures a prendre dans de telles circonstances. 

C'est le Comite d' experts des insectes nuisibles aux animaux (Agriculture 
Canada) qui a eu l'idee de ce contrat, et quelques-uns de ses experts ont 
permis de mener a bien ce projet. Vous trouverez ci-apres les noms de ces 
membres et des autres collaborateurs, ainsi que leurs coordonnees et les 
sections de l'ouvrage qu'on leur a confiees. 

D r R.A. Brust - Departement d'entomologie, Universite du Manitoba, Winnipeg 
(Man.) R3T 2N2. Partie I. Sections 3a (i, ii, iii, iv), 4a (iii, iv) , 
4b (i, ii), 4c (i, ii, iii), 6a (iv, v), 7b. 

D r R.A. Costello - British Columbia Ministry of Agriculture and Fisheries, 

1770-57th avenue, Surrey (C.-B.) V3S 1Z4. Partie I. Section 4a (i, ii). 

D r R.A. Ellis - Prairie Pest Management, 207 Cullen Dr., Winnipeg (Man.) 
R3R 1P5. Partie I. Sections 6a (i, ii, iii), 6b, 7a, c, 9a, b, c, d; 
Partie II. 2, 3; Annexes I, II et III. 

D r M.M. Galloway, directeur, Centre canadien sur les insectes piqueurs, 
Departement d'entomologie, Universite du Manitoba, Winnipeg (Man.) 
R3T 2N2. Partie I. Sections 4d (i), 5a; Partie II, la, b, c, d; 
Annexe IV. 

D r T.D. Galloway, Departement d'entomologie, Universite du Manitoba, 
Winnipeg (Man.) R3T 2N2. Partie I. Sections 2a (i, ii, iii, iv) , 
3b, c, d, 4b (iii), 4d (ii), 5b. 

D r W.L. Lockhart, ministere des Peches et des Oceans, Institut des 
eaux douces, 501 University Crescent, Winnipeg (Man.) R3T 2N6. 
Partie I. Sections 8a, b, c. 

D r P.N. Nation, Head, Veterinary Pathology Branch, Alberta Agriculture, 
6909 116 St., Edmonton (Alb.) T6H 4P2. Partie I. Sections 2a (i), 
donnees concernant 1' Alberta au tableau 2. 



D r H.J. Smith, Direction generale de la production et de 1' inspection des 
aliments, Direction de l'hygiene veterinaire, Division de la 
pathologie animale, Case postale 1410, 13, rue College, Sackville 
(N.-B.) EOA 3C0. Partie I. Sections 2c (i, ii, iii). 

D r G.A. Surgeoner, Dept. of Environmental Biology, University of Guelph, 
Guelph (Ont.) NIG 2W1. Partie I. Sections 2b (i, ii, iii, iv) . 



Le projet en question a ete finance dans le cadre d'un contrat 
qu' Agriculture Canada a passe avec le Centre canadien sur les insectes 
piqueurs. 

Nous temoignons notre reconnaissance au doyen actuel de la Faculte 
de 1' agriculture de l'Universite du Manitoba, M. J.I. Elliot et a son 
predecesseur, M. R.C. McGinnis, ainsi qu'au Bureau de 1' administration de la 
recherche de l'Universite du Manitoba pour leur soutien et leur aide 
financiere. Nous remercions aussi le D r R. Trottier, president du Comite 
d 1 experts des insectes nuisibles aux animaux (Agriculture Canada) et son 
predecesseur, M. R.M. Prentice, de leur precieuse contribution. 



2. DISEASES 

a. Western Equine Encephalitis 
i. History 

The early recognition of WEE virus as a disease -causing 
agent was understandably difficult. Clinical symptoms are not 
glaringly unique and most often occur in horses and humans . 
Association of a common causative agent in these two diverse hosts 
was not easily accommodated. Disease outbreaks have historically 
been sporadic, interspersed by periods of virtual absence of 
clinical activity. Detection and isolation of virus required 
special handling of affected tissues. Epidemics and epizootics 
have not always coincided closely. Consequently, the first 
isolation of WEE virus by Meyer et al. (1931) from horses, and 
confirmation of the relationship of this same virus to human 
encephalitis by Howitt (1938) were landmarks in an understanding 
of this disease. 

The WEE virus is apparently widespread in Canada and human 
cases have been reported from British Columbia, Alberta, 
Saskatchewan, Manitoba and Quebec (Artsob and Spence 1979, Table 
1) . However, the Prairie Provinces have been the prime focus for 
both human and equine infections. For the total number of 1607 
confirmed human cases reported from Canada, 865 (54%) and 674 
(42%) occurred in Saskatchewan and Manitoba, respectively. Over 
68% (1094 cases) of all human cases were recorded during a single 
epidemic in the prairies in 1941 (Table 1) . 

Epizootics of WEE in horses were recognized in Canada for 
many years before the causative agent was isolated and identified 
in 1935 by Fulton (1938). Previous to 1935, it was known that 
horses suffered from an affliction of the nervous system, but were 
diagnosed in somewhat vague terms as having forage poisoning, 
botulism, cerebro- spinal meningitis, corn-stalk disease, sleeping 
sickness or blind staggers (Fulton 1938; Artsob and Spence 1979). 
As for WEE in humans , cases of WEE in horses are widespread in 
Canada, reported from British Columbia, Alberta, Saskatchewan, 
Manitoba and northwestern Ontario (Table 2; Artsob and Spence 
1979) . Many thousands of horses were lost to WEE in Saskatchewan 
and Manitoba, again the provinces where clinical disease in horses 
has been most prevalent. The development of an effective vaccine 
for horses, introduced in 1938, seems to have limited the relative 
magnitude of epizootics. For example, it was estimated that 9% of 
the Manitoba horse population was clinically affected in the 
outbreak of 1937 (data collected by questionnaire circulated to 
70 municipalities) (Savage 1942). Since the widespread 
availability of the WEE vaccine, the incidence of WEE has not 
approached even 1% of the total horse population. 

It is fair to assume that Public Health personnel and 
veterinarians will face isolated cases and outbreaks in the 
future. Increased awareness of WEE in recent years should result 
in rapid diagnosis and optimal treatment in the majority of cases. 



ii. Nature of Disease 

Western Equine Encephalitis virus is an Alphavirus in the 
Togaviridae. There are apparently three serologically similar 
variants of WEE virus, only one of which, WEE virus sensu 
sCricta, will be considered here. The other two are Highlands J 
virus and Fort Morgan virus . Highlands J virus was once thought 
to be a less virulent strain of WEE virus, found in the eastern 
U.S. and Gulf Coast states, and is in many ways ecologically 
reminiscent of WEE virus (see Hayes and Wallis 1977 for a review) . 
Fort Morgan virus has so far been recovered only from the cliff 
swallow - English sparrow -swallow bug system in the west central 
U.S. (Calisher et al. 1980). 

WEE virus is widespread in the New World. It is most 
prevalent and best known in the western and south central U.S. and 
Prairie Provinces , where there have been numerous outbreaks in 
humans and horse populations since recognition of the disease. 
However, the virus is also prevalent in South America, and 
outbreaks are known in Brazil, Guyana, Uraguay and Argentina 
(Grimstad 1983) . 

The enzootic cycle of WEE virus involves mosquitoes as 
primary vectors and wild avian hosts. This cycle has been studied 
in greatest detail in foci in California and Texas where Culex 
tarsalis is the most important vector for the virus. Nestling 
passerines are the principal amplfying factor for the virus, and 
horizontal transfer continues throughout the bird population as 
long as there are sufficient susceptible hosts and vector 
mosquitoes . 

Epizootics and epidemics are initiated when the prevalence 
of virus in the endemic cycle increases, and probability of horses 
and humans contacting infected vectors is high. Clinical symptoms 
in horses and humans may or may not be present, but the duration 
and level of viremia are insufficient to warrant their 
contributing significantly to the amplication or persistence of 
the virus. Unfortunately, the consequences of clinical WEE in 
these cases can be serious, resulting in death or permanent 
physical and behavioural disability. 

Involvement of humans and horses in the WEE disease cycle 
has prompted a great deal of intensive research activity. 
However, one aspect of the disease remains enigmatic and offers 
room for considerable speculation. There is still no convincing 
evidence for the support of an overwintering mechanism. 
Transovarial transmission in mosquitoes, mites and bird is 
apparently negative. The virus may be capable of overwintering in 
adult female mosquitoes, but evidence so far is weak. Vectors 
other than Culex tarsalis may be important, perhaps Culiseta spp. , 
Anopheles spp. or even spring Aedes spp. , but their role is 
unclear. It has been suggested that hibernating vertebrates may 
be able to harbour the virus through the winter and display a high 
or cyclic viremia when they resume activity in the spring. 
Snakes, frogs, turtles, and ground squirrels have all been 
considered possible candidates, but there is no clear support from 



field data. Migratory birds may carry chronic latent infections 
and display a viremia at the onset of reproductive activity, or 
may become infected in the south and carry a virus infection with 
them on their northward flight. Again, however, these mechanisms 
are speculative in regard to the establishment of new disease foci 
or generation of epidemic cycles. It has also recently been 
suggested that infected mosquitoes may be borne considerable 
distances on prevailing winds from endemic foci into non-endemic 
regions. Clearly, the question of overwintering of WEE virus 
should provide a significant objective for future research in the 
field. 

In Canada, epidemics have been sporadic and rarely involved 
large numbers of people. Even though consequences of clinical 
disease can be severe, it is difficult to justify continued 
expenditure of public funds in support of the long term field and 
laboratory research necessary before we can gain a good 
understanding of the epidemiology of WEE. With the inevitable 
occurrence of epidemics in the future, it seems unlikely that 
researchers and medical personnel will be able to provide the 
answers to questions asked by the public and political decision 
makers . 

ill. Clinical Aspects in Human Infections 

Humans and horses play no major role in the epidemiology of 
WEE virus. However, because of the severe clinical manifestations 
of disease in these dead-end hosts, and the frequency and 
magnitude of outbreaks in the Prairie Provinces (see Tables 1, 2), 
WEE must be considered, historically, the most important mosquito- 
borne virus in Canada. During epidemics of WEE, there has been 
ample opportunity to document closely, the onset and development 
of symptoms, pattern of recovery, sequelae, and pathology. 

The onset of clinical symptoms of WEE may be gradual, 
increasing in intensity or may be sudden, especially in young 
children and infants. In most cases, acute illness is preceeded 
by headache, fever, drowsiness and gastrointestinal disturbance 
(Pavilanis et al. 1957; Friesen and Eadie 1982). With the 
exception of headache, these symptoms are generally mild and cause 
for little concern in patients. The intense and persistent 
headache may last for several days, prompting the person to seek 
medical attention. Upon examination, the patient displays 
symptoms more closely associated with flu virus infection than 
central nervous system involvement (Adamson and Dubo 1942) . 

The acute phase of WEE presents an array of non-specific 
central nervous system disorders, and may last, on average, three 
weeks (Gareau 1941). Headache may persist, in a high percentage 
of cases, accompanied by a variably high fever running from 38.4 - 

40.4° C (Waters 1976). The febrile period may last from 7-10 
days before returning to normal. Convulsions and delerium 
commonly accompany periods of high fever, and may not necessarily 
be associated with direct damage to the brain by virus infection. 
Convulsions more commonly seem to accompany infections in infants 
(Adamson and Dubo 1942; Medovy 1943). 

10 



Cerebrospinal fluid may be under pressure infrequently or 
for short duration, and is rarely severe. All counts are 
generally elevated and may persist in such condition throughout 
the acute phase. The cell content is dominated by 
polymorpholeucocytes early in the infection, gradually falling to 
normal after about 4 days (Adamson and Dubo 1942). Mononuclear 
cells generally predominate after 3-4 days. Total cell counts 
reach their highest levels during the first few days (averaging 
150; as high as 400 or more) (Adamson and Dubo 1942), and remain 
elevated for at least 9-10 days. 

There are a variety of non-specific associated symptoms 
during the acute phase. Most patients experience some degree of 
sleep disturbance, predominately somnolence, though examples of 
insomnia are not uncommon. There may be a degree of muscle pain 
or stiffness and like stiffness of the spine, is generally not 
severe, and not of great concern to the patient. Muscle 
discomfort apparently lasts only 4-5 days during the acute phase 
(Adamson and Dubo 1942). Medovy (1943) reported that, in infants, 
a peculiar rigidity, which was accompanied by high fever and 
general restlessness, was one of the earliest symptoms observed 
and lasted the longest. 

Patients are frequently anorexic, and experience nausea and 
abdominal cramps (Gareau 1941) . Vomiting is prevalent among 
patients but is not usually frequent or peristent. Those people 
who suffer vomiting generally do so for only one day. Bladder and 
bowel disorders are common and constipation may require frequent 
attention and treatment. 

Tremors, characteristically in the facial muscles, lips and 
tongue are frequently reported and Adamson and Dubo (1942) 
considered these signs valuable in diagnosing WEE as opposed to 
polio during the 1941 epidemics. Some degree of speech impediment 
occurs, largely due to the disfunction of facial and throat 
muscles, and speech may be slurred or very slow. The face in 
general may take on a flushed or masked appearance or have an 
overall puffiness. The nose may be red, and the eyes inflamed. 
Sweating during this phase may be profuse and patients frequently 
experience chills as well (Adamson and Dubo 1942 ; Friesen and 
Eadie 1982) . 

In severe cases, patients may suffer a distinct loss of 
motor control and coordination (Friesen and Eadie 1982) . 
Paralysis is not frequent and is not usually severe or widespread. 
Patients commonly exhibit at least dulling of the senses or mental 
confusion to a general stupor. In the extreme, 10-20% of clinical 
cases, patients may become comatose for variable periods of time, 
often up to 3 or 4 days (Adamson and Dubo 1942; Friesen and Eadie 
1982) . One of the remarkable clinical features of WEE is that a 
person may suffer from this extended period of coma, and still 
recover fully. 

Unfortunately, the various signs and symptoms described 
above appear to be of little prognostic value. Death has occurred 
in approximately 10% of the reported clinical cases in Canada (see 
Table 1) . Highest mortality rates seem to be associated with 

11 



cases involving infants (less than 1 year old at the time of 
infection), and the elderly, often following respiratory or 
gastrointestinal complications. 

Patients may recover fully following the acute phase of the 
infection, or exhibit varying degree of sequelae. Most studies 
have included examination of patients within a year of release 
from hospital. In these studies, a high proportion of patients 
still suffer from residue such as subtle changes in mood or 
personality, fatigue, slight tremors or twitches, slight loss of 
fine and/or gross motor control, inability to concentrate, 
sleep/rest disorders, or sensory distortion, involving hearing, 
speech or taste (Mulder et al. 1952; Friesen and Eadie) . 
Occasionally, there may be severe psychological disturbance that 
may restrict normal social interaction or necessitate 
institutionalization (Fulton and Burton 1953; Earnst et al. 1971). 
Neurologic sequelae including convulsions, spastic weakness or 
brain disfunction may also be apparent (Earnst et al. 1971). 
Mulder et al. (1952) and Hawryluk et al. (1982) felt that severity 
of sequelae, at least among adult patients, could be directly 
correlated with duration of the comatose period or degree of 
debility during the acute phase of the disease. 

In summary, WEE is a virus disease characterized by a 
complicated and variable pattern of onset and acute phase. 
Accurate confirmation of diagnosis cannot usually be made on the 
basis of the clinical picture, and medical authorities must rely 
on a serological diagnosis. Recovery may be rapid and complete, 
but in some patients sequelae occur which may be mild to severe . 
The recovery period often requires more than a year, and in cases 
where permanent damage has occurred patients never fully recover. 

Pathology in humans following WEE virus infection seems 
largely to be restricted to the brain and central nervous system. 
At the time of autopsy, the organs appear generally unremarkable, 
or perhaps slightly oedematous (Quong 1942) . There is no gross 
haemorrhage associated with brain tissues and there are no obvious 
diagnostic characteristics. 

Quong (1942) identified three categories of microscopic 
change associated with the nerve tissues following post mortem 
examination on 18 human cases during the 1941 epidemic in 
Manitoba. The leptomeninges were oedematous and separated, 
containing scattered lymphocytes and glial cells. Perivascular 
cuffing, also observed by Rozdilsky et al. (1968), was evident, 
with lymphocytes and glial cells predominating. Finally, there 
were numerous small (0.2-0.4 mm), scattered areas of cell 
breakdown and deterioration. These lacunae eventually become 
filled with small cells, but were often seen as clear areas in 
histological preparations and gave the tissues what Quong (1942) 
referred to as a moth-eaten appearance. He even suggested that 
because the areas of damage were so small and scattered, that this 
may account for the relative freedom of serious sequelae in the 
majority of humans who recovered from the acute phase of the 
disease. Quong (1942) found that the grey matter was most 
seriously affected, while Rozdilsky et al. (1968) observed similar 

12 



tissue destruction more extensively in the white matter. 

Pathology, therefore, is quite restricted to the central 
nervous tissues. However, Monath et al . (1978) discovered that 
they could produce myocarditis and impaired cardiac function in 
mice infected with WEE virus. To date, there is no evidence to 
support similar cardiac involvement in humans. 

iv. Epidemiology 

By the very nature of Western Equine Encephalitis outbreaks 
in humans in Canada, it is difficult to assemble a meaningful 
epidemiological picture. The epidemics are sporadic and often do 
not encompass large numbers of clinical human cases (see Table 1) . 
The majority of the data summarized below were collected during 
the outbreaks in the Prairie Provinces in 1941 (1094 cases) , 1975 
(14 cases) and 1981 (25 cases). 

The 1941 Epidemic 
Introduction 

By virtue of the relative magnitude of the 1941 epidemic, we 
can gain better understanding of the epidemiology of WEE as it 
affects humans, than in any other epidemic period in Canada. The 
data collected during 1941 were reported for Alberta by McGugan 
(1942) , for Saskatchewan by Davison (1942) , and for Manitoba by 
Donovan and Bowman (1942a, b) and most of the following discussion 
is drawn from these sources. Coincident with the WEE epidemic, 
the Dominion Bureau of Statistics conducted their eighth national 
census on 2 June , 1941 , and was the source of demographic 
information (Vol. I 1950; Vol III 1946). 

Canada was in a period of turmoil in 1941. The country had 
passed through a period of severe economic and industrial 
depression. On the prairies, there was a reduced farm population 
and the numbers of marriages and births had declined. For the 
first time in Canada's history, the population below age 10, 
failed to exceed the 10-19 age class size. Immigration into 
Canada was reduced and industrial centres were faced with acute 
housing shortages. 

By 1941, the economy showed signs of improvement, but Canada 
was at war, and approximately 313,452 males were enlisted in the 
Armed Forces at the time of the census in June . As a consequence 
of the depleted young male population and the increasing demand 
for food and supplies, changes took place in the previous 
employment pattern. More women were drawn into the active work 
force, and the average age of farm operators increased. The 
training activity of Armed Forces personnel resulted in widespread 
movement of troops, many of which came to bases on the Prairies, 
in rapidly prepared camp and barrack environments where men were 
concentrated in high densities. 

Medical personnel in the Prairies were on the alert as the 
summer of 1941 unravelled. What was described as a major 
poliomyelitis epidemic in Manitoba and Alberta, began in June, and 
continued until early November, with 966 reported cases. Many of 
the early WEE cases were initially diagnosed as poliomyelitis. 

13 



The temporal course of the WEE epidemic in the summer of 
1941 was similar among the three provinces involved. 
Saskatchewan, with 543 cases, reported the greatest spread from 
first to last dates of onset. One case in April, one in May and 
additional cases in June all occurred before any clinical activity 
was observed in either Alberta or Manitoba. No onset of WEE was 
reported from the latter provinces until late July. The peak in 
numbers of cases reported was uniformly in mid to late August. In 
Manitoba and Saskatchewan 195 (38%) and 180 (33%) of the cases 
were reported in weeks ending 19 and 23 August, respectively. By 
autumn, the incidence of WEE declined, until no further human 
cases occurred beyond 10 September, 14 October and 15 November for 
Alberta, Manitoba and Saskatchewan, respectively. 

The data on numbers of clinical cases of WEE in humans, 
according to age and sex, were not reported in consistent fashion 
among provinces. Consequently, these data are summarized here 
(Table 3) according to three quite broad age categories i.e. 
infants (<1 year of age), adolescents (ages 1-20) and adults (>20 
years of age) . For Alberta, McGugan (1942) provided no 
information on sexes by age of patients, other than that of the 
total, 30 (71.4%) were males and 12 (29.6%) were females. Data 
for Manitoba and Saskatchewan were more complete, but authors used 
different age groupings in reporting numbers of cases. 

Geographic Distribution 

As pointed out by Donovan and Bowman (1942a, b) there was no 
real spread of WEE in the 1941 epidemic, in the sense that human 
cases did not radiate out from isolated foci. Rather, cases were 
reported in seemingly random fashion from throughout the affected 
area. 

Most cases of WEE were, however, from the southern region of 
the Prairie Provinces . For example , approximately 80% of the 
human cases in Manitoba occurred south of 50° N latitude, and 
about 72% in Saskatchewan were in south central areas of the 
province, south of Regina. In Alberta, 75% were reported from the 
southeastern corner of the province. In Manitoba cases were 
reported from as far north as the Swan River area in the western 
region, and Fisher Branch and Chattfield areas in the Interlake. 
In Saskatchewan, there was one case reported from the Meadow Lake 
area, along with 7 cases from Saskatoon. 

There was a rural bias in the reported human cases in the 
1941 epidemic. Approximately 80% of the Manitoba cases were from 
outside the most densely populated urban areas. Despite half the 
population of the province residing in Winnipeg and suburbs, less 
than 1/3 (166 cases) of the cases occurred there. Similarly in 
Saskatchewan nearly 2/3 of the total cases were from rural areas . 
As one would assume from these statistics, the outdoor workers 
seemed to be at greatest risk of exposure. In Alberta > 90% of 
the clinical cases were farm family members (Davison 1942; Donovan 
and Bowman 1942a, b; McGugan 1942). 



14 



Age Distribution and Sex Ratios 

Very little can be deduced from the WEE epidemic in Alberta 
in 1941. Only 42 total human cases were reported, and these only 
in the 1-19 year and > 19 year age classes. No infants developed 
clinical symptoms, and number of clinical cases in the older age 
classes did not exceed 0.1/1000 (0.07 and 0.04 for the 1-19 and > 
19 year age classes respectively) . 

The population of Saskatchewan exceeded that in Manitoba for 
all age classes (Table 4) , but the proportions of each sex were 
approximately equal. In both provinces, infants most often 
exhibited clinical symptoms (2.7 and 2.1/1000 for Saskatchewan and 
Manitoba respectively) although these data did not necessarily 
correlate with the proportion of deaths (Table 3) . Adolescents 
were least affected in terms of manifested clinical signs, with 
only 0.4 and 0.3/1000 for Saskatchewan and Manitoba respectively. 
In Saskatchewan proportionally fewer people in the adult age class 
became ill (0.7/1000), compared to Manitoba (0.9/1000). However 
in both provinces over 30% of the total reported WEE cases 
occurred in the over 45 age classes, where only about 20% of the 
total population was included. 

The proportion of clinical cases among infants was 
approximately equal for males and females in both Saskatchewan and 
Manitoba (Table 3). In the older age classes, where sex specific 
occupational differences are expected to be more pronounced, the 
proportion of cases in males greatly exceeded that among females 
(Table 3). For Saskatchewan and Manitoba combined, nearly 69% of 
the total cases in the adolescent and adult age classes were male. 

Occupational Relationships 

No quantitative analysis of occupation for each of the 
reported WEE cases was published for the 1941 epidemic. McGugan 
(1942) did determine that "slightly over ninety per cent of all 
reported cases occurred among farmers and farmers' families". 
Davison (1942) suggested that because the peak of pathogen 
transmission occurred during the summer holiday season, many of 
the urban infections may have been acquired during visits to rural 
or recreational areas . 

The 1975 Epidemic 
Introduction 

By comparison to the widespread 1941 epidemic of WEE in the 
Canadian Prairie Provinces, subsequent disease activity among 
human populations in Canada has been insignificant. However, 
epidemics in Manitoba in 1975 and again in 1981 were intensively 
studied and co-ordinated efforts were made to maximize the amount 
of information gathered. In 1975, there were only 14 confirmed 
human cases, all in Manitoba (Waters 1976). The earliest 
confirmed case was reported during the first week of August, and 
the last after 6 September. The largest number of cases (6) for 
any week occurred during the period 23-29 August. No deaths were 
attributed to WEE virus in 1975. Because of the small number of 

15 



cases, conclusions regarding peak activity, age and sex class 
affected, and geographic pattern are limited, but are summarized 
here as for the 1941 outbreak. 

Geographic Distribution 

Seven cases were reported in patients who lived in Winnipeg 
or on the outskirts. The remainder were distributed throughout 
southern Manitoba, the most northerly human case from Gimli. 

Age Distribution and Sex Ratio 

All age groups were affected in the 1975 outbreak. Two 
cases, both males, occurred in infants; six patients (3 males; 3 
females) were adolescents; six (4 males; 2 females) were adults. 
There was an overall preponderance of cases among males (9 vs. 5 
females) , but the small number of cases makes conclusions 
questionable . 

Occupational Relationships 

No data were reported on the occupation of the various 
patients during 1975. 

The 1981 Epidemic 
Introduction 

In 1981, the only clinical human WEE cases reported in 
Canada occurred in Manitoba and were described in great detail by 
Friesen and Eadie (1982), Hawryluk et al. (1982), and Eadie and 
Friesen (1982). Of the 25 human cases in 1981, 22 were 
interviewed in person or by telephone, and the additional 
information gained from relatives, friends, neighbours and 
colleagues (Eadie and Friesen 1982) , to produce the most complete 
epidemiological profile of any Canadian WEE outbreak. As in 1975, 
the total number of cases (25), with two deaths, does not allow 
extensive analysis. 

The first case occurred on 13 July, and numerous cases were 
reported sporadically until the last onset on 10 October (Sekla 
and Stackiw 1982) . The greatest number of cases was recognized 
during the period 10-24 August (9 cases), but three cases per week 
occurred during the other weeks of August. 

Geographic Distribution 

Twelve of the total human cases were either from Winnipeg (5 
cases) or other urban Manitoba areas (7 cases). The remaining 13 
were from rural areas. There were no apparent foci of infection, 
all cases being widely distributed. The northernmost case was 
just south-west of Swan River. There were no cases in either the 
Interlake Region, or in the eastern boreal forest zone of the 
province . 

Age Distribution and Sex Ratio 

There was one male infant case and two male adolescents 

cases in 1981. The remaining cases were 18 adult males, and 4 

adult females. There was a preponderance of male cases in all age 

16 



classes . 

Occupational Relationships 

Farm workers were a dominant component of the clinical cases 
in 1981. Ten patients were defined as full time farmers, and on 
average spent more time outdoors than the average for all other 
patients. Three additional cases were part-time farmers. The 
remaining cases were distributed among various occupations. 



Conclusions 

The outbreaks of clinical WEE in humans in Canada have been 
sporadic, and with the exceptions of 1941, 1975 and 1981, less 
than extensively reported. Among these three years, the 1941 data 
alone contains enough cases from which we can draw conclusions, 
but trends in both 1975 and 1981 in Manitoba are supportive. 

With the exception of a few very early and very late cases 
seen in 1941 in Saskatchewan, it seems one can expect the first 
cases to appear in the latter part of July, with peak clinical 
activity in August. The rate of appearance of new cases would be 
expected to subside in September, with perhaps a few late cases in 
October. At the moment there is no available means to predict 
either number or location of cases. Since a large proportion of 
the population is susceptible to WEE virus, presumably exposure to 
the pathogen is related to probability of contact with infected 
mosquito vectors. Although a greater proportion of reported 
clinical cases are males, presumably this bias is a reflection of 
a greater probability of contact with vectors, rather than some 
intrinsic factor. Factors affecting manifestation of disease 
symptoms are unknown, but infants seem to be particularly 
sensitive to infection. 



17 



Table 1. Numbers of human clinical cases of WEE reported for each 
province in Canada, 1935-1986. There were no cases reported in 
years not cited. 



Province 


Year 


No. of Cases 


No. of Deaths 


British Columbia 


1971 


5 




2 1 




1971 


14 




O 2 


Alberta 


1941 


42 




8 3 




1963 


6 




0* 


Saskatchewan 


1935-7 


present 


N 


.A. 5 




1938 


29 




4 6 




1939 


few 




l 5 




1941 


543 




44 5 




1947 


68 


N 


.A. 7 




1953 


53 


N 


.A. 8 




1963 


90-100 




3 7 




1964 


1 




9 




1965 


72 




8 io 




1966 


2 




9 




1967 


1 




9 




1969 


1 




o 9 


Manitoba 


1938 


27 




6 11.12 




1941 


509 




7gll,12,13 




1947 


81 


N 


.A. 14 




1975 


14 




15 




1977 


5 




16 




1981 


25 




216 


• 


1983 


18 




I 17 



Ontario 

Quebec 1955 



as 



^ettyls et al . (1972); 2 Kettyls and Bowmer (1975); 3 McGugan 
(1942); A Morgante et al. (1968); 5 Fulton (1941); 6 Davison (1942); 
7 Dillenberg (1965); 8 Dillenberg et al. (1956); ^cLintock et al. 
(1979); 10 Rozdilsky et al. (1968); n Donovan and Bowman (1942a); 
12 Donovan and Bowman (1942b); 13 Jackson (1942); u Snell (1966); 
15 Sekla and Stackiw (1976); 16 Sekla and Stackiw (1982); 17 Sekla 
(unpublished); 18 Pavilanis et al. (1957). 



18 



Table 2 . Numbers of confirmed WEE equine cases reported for each 
province in Canada, 1935-1986. There were no cases confirmed in 
years not cited. 



Province 



Year 



No. of Cases No. of Deaths 



British Columbia 



Alberta 



Saskatchewan 



Manitoba 



1971 


60 


15 l 


1972 


17 


N.A. 2 


1973 


7 


N.A. 2 


1965 


136 


N.A. 3 


1977 




4 2° 


1980 




1 20 


1981 




17 20 


1982 




^ 20 


1983 




■t 20 


1935 


extensive 


N.A. 4 


1937 


extensive 


N.A." 


1938 


-52,500 


>15,000 5 


1941 


present 


N.A. 6 


1953-4 


76 


N.A. 7 


1962 


extensive 


N.A. 8 - 9 


1963 


279 


47 9 


1964 


41 


N.A. 10 


1965 


106 


N.A. 10 


1966 


8 


N.A. 10 


1967 


10 


N.A. 10 


1968 


9 


N.A. 10 


1969 


40 


N.A. 10 


1970 


17 


N.A. 10 


1971 


7 


N.A. 10 


1974 


4 


N.A. 10 


1975 


23 


N.A. 10 


1981 


2 


N.A. 10 


1935 


extensive 


N.A. 4 


1937 


-12,000 


>2,000 12 


1938 


extensive 


N.A. 12 


1941 


present 


N.A. 6 


1963 


173 


N.A. 13 


1964 


73 


N.A. 13 


1965 


75 


9 14 


1966 


51 


N.A. 15 


1968 


14 


N.A. 13 


1969 


41 


N.A. 13 


1975 


145 


N.A. 13 - 16 


1976 


10 


N.A. 16 


1977 


53 


N.A. 16 



19 



2 (Continued) 



Province 


Year 


No. of Cases 


No. 


of deaths 




1978 


1 




N.A. 16 




1980 


1 




N.A. 16 




1981 


120 




N.A. 16 




1982 


1 




N.A. 17 




1983 


23 




N.A. 17 


Ontario 


1937 


1 




1 18 




1975 


4 




N.A. 13 




1981 


2 




N.A. 19 



Kettyls et al . (1972); 2 Kettyls and Bowmer (1975); 3 Morgante et 
al. (1968); A Fulton (1938); 5 Davison (1942); 6 Cameron (1942); 
7 Dillenberg et al. (1956); 8 Spalatin et al. (1963); 
9 Dillenberg(1965); 10 Spalatin et al. (1963); 9 Dillenberg (1965); 
10 McLintock et al. (1979); n Neufeld and Nayar (1982); 12 Savage 
(1942); 13 Lillie et al. (1976); u Snell (1966); 15 McKay et al. 
(1968); 16 Sekla and Stackiw (1982); 17 Sekla (unpublished); 
18 Mitchell and Walker (1941); 19 Surgeoner et al. (1982); 20 Nation 
(unpublished) . 



20 



Table 3. Summary of numbers of clinical human case and deaths by 
age and sex in the Western Equine Encephalitis epidemic in the 
Canadian Prairie Provinces, 1941. 





Alberta 1 


Saskatchewan 2 


Manitoba 2 


Age/ 


No. of 


No. of 


No. of 


No. of 


No. of 


No. of 


Class 


Cases 


Deaths 


Cases 


Deaths 


Cases 


Deaths 




(%) 


(%) 


(%) 


(%) 


(%) 


(%) 


<1 vr. 














Male 


- 


- 


24 





13 


2 








(55.8) 


(-) 


(48.2) 


(66.7) 


Female 


_ 


- 


19 





14 


1 








(44.2) 
45 


(-) 




(51.8) 
27 


(33.3) 


Total 








3 




(-) 


(-) 


(8.3) 


(-) 


(5.3) 


(11.1) 


l-19vr. A 














Male 


- 


- 


89 


2 


49 


4 








(59.3) 


(40.0) 


(69.0) 


(44.4) 


Female 


_ 


_ 


61 


3 


22 


5 








(40.7) 
151 


(60.0) 
5 


(31.0) 
71 


(55.6) 


Total 


20 





9 




(47.6) 


(-) 


(27.8) 


(3.3) 


(14.0) 


(12.7) 


>19vr* 














Male 


- 


- 


246 


21 


289 


37 








(71.1) 


(55.3) 


(70.3) 


(56.1) 


Female 


- 


- 


100 


17 


122 


29 








(28.9) 


(44.7) 


(29.7) 


(43.9) 


Total 


22 





346 


38 


411 


66 




(52.4) 


(-) 


(63.9) 


(11.2) 


(80.7) 


(16.1) 


TOTAL 














Male 


- 





359 


23 


351 


43 






(-) 


(66.6) 


(53.5) 


(69.0) 


(55.1) 


Female 


. 





80 


20 


158 


35 






(-) 


(33.4) 


(46.5) 


(31.0) 


(44.9) 


TOTAL 


42 





543 


43 


509 


78 



^cGugan (1942); 2 Davison (1942); 3 Donovan and Bowman (1942a, b) 
A No. of cases and deaths not reported according to sex for 
Alberta. 



21 



Table 4. Breakdown of the human population by age and sex for 
the Canadian Prairie Provinces according to the 1941 Dominion of 
Canada census . 



Age/Class 


Alberta 


Saskatchewan 


Manitoba 


< lyr. 








Male 


7,756 


8,761 


6,571 


Female 


7.452 


8.269 


6.360 




15,208 


17,030 


12,931 


1-19 yr. 








Male 


147,177 


176,322 


127,205 


Female 


144.425 


170.723 


124.236 




291,602 


347,045 


351,441 


> 19 yr. 








Male 


271,525 


292,480 


244,303 


Female 


271.834 


239.427 


221.069 




489,356 


531,907 


465,372 


Total 








Male 


426,458 


477,563 


378,079 


Female 


369.711 


418.429 


351.665 




796,169 


895,992 


729,744 



22 



b. St. Louis Encephalitis 

Several excellent reviews on St. Louis Encephalitis have 
been published, primarily in response to a widespread epidemic of 
the disease throughout the central and eastern United States and 
southern Ontario in 1975 (Creech 1977) . Important reviews include 
Luby 1979, Monath 1980, Kemp 1981, Tsai and Mitchell (1989). 
Mahdy et al. (1979) reviewed the response to the 1975 outbreak 
in southern Ontario and is of greatest relevance to Canada. This 
chapter is a review of the status of St. Louis Encephalitis in 
Canada with particular reference to findings since the 1975 
outbreak. 

i. History 

St. Louis Encephalitis (SLE) was first recognized as a 
clinical disease in 1933, during a large epidemic in the central 
United States centered around St. Louis, Missouri (Chamberlain 
1980) . The first evidence of SLE in Canada was determined by 
serum neutralization tests of a 71-year-old female in Manitoba in 
1941 (Donovan and Bowman 1942a, b). A further case was indicated 
using complement fixation in Saskatchewan in 1954 (Dillenberg et 
al. 1956). No further cases were identified in Canada until the 
major epidemic of 1975. 

In 1975, 66 cases of SLE including five fatalities were 
reported from southern Ontario (Spence et al. 1977). Single cases 
were reported from Quebec (Davidson et al. 1976) and Manitoba 
(Sekla and Stackiw 1976) . An additional four cases were detected 
in southern Ontario during 1976 (Weekly Bulletin, Community Health 
Protection Branch, O.M.H. , October 8, 1976). 

To the author's knowledge there have been no reported cases 
in Canada since 1976. In serological surveys of ca. 4,000 
individuals from southern Ontario within 12 months after the 1975 
epidemic, ca. 0.8% of the residents had antibodies to SLE as 
detected by Haemagglutination Inhibition (HAI) tests (Artsob et 
al. 1979). Neutralizing antibodies have been found in residents 
of Saskatchewan (McLintock 1976), Alberta (Hoff et al. 1970), and 
British Columbia (Kettyls et al. 1972). 

The SLE virus was first isolated in Canada from a pool of 
Culex tarsalis mosquitoes collected in Saskatchewan (Burton et al. 
1973) . The virus has also been isolated from Culex pipiens 
collected in southern Ontario during 1976 (Thorsen et al. 1980) 
and from the brain tissue of a fatal case in southern Ontario 
during 1975 (Spence et al. 1977). 

In addition, antibodies to SLE have been detected in 
migratory birds in Ontario (Karstad 1965) prior to the 1975 
epidemic. In southern Ontario in 1976 12. 82 of the migratory 
birds tested were positive for SLE but none in the subsequent two 
years (Dorland et al. 1979). Similarly, during limited 
surveillance of English sparrows in the fall of 1975 and early 
1976, (29.8%) of 57 English sparrows were seropositive for SLE 
(Dorland et al. 1979). Since 1977, over five summers of sentinel 

23 



monitoring, no evidence of SLE antibody has been detected from ca. 
1,000 sera per year of either English sparrows or sentinel 
chickens (pers. obs.). In other areas of Canada, antibodies have 
also been detected from moose, bull snakes and snowshoe hares in 
Alberta and from birds and small mammals in British Columbia (see 
Artsob and Spence 1979) . 

SLE virus is probably not endemic to Canada but enters as a 
northern extension of activity in the central or western United 
States. The cyle in western Canada would involve Culex tarsalis 
and that in eastern Canada Culex pipiens and Culex restuans as 
primary vectors. 

ii. Nature of Disease 

St. Louis Encephalitis is an RNA virus belonging to the 
family Togavuidae in the genus Flavivirus group with close 
antigenic relationships to Japanese Encephalitis, West Nile and 
Murray Valley virus (Karabatsos 1980). Serological cross- 
reactions with such viruses as Dengue -2 and Yellow Fever virus may 
create false positive reactions by (HAI) or Immunoflourescence 
(IF) techniques. Monoclonal antibody and neutralization tests may 
be necessary for confirmation of antibodies (Roehrig et al. 1983). 
Six strains of SLE virus have been identified (Trent et al. 1980) 
with varying degrees of virulence (Monath et al. 1980). The 
strain collected from the central United States during 1975 had 
high virulence in mice, whereas a strain from the western United 
States had lower virulence (Monath et al. 1980). Actual strain 
determination of field isolates is therefore important in 
determining the potential virulence of the virus to humans. 

The virus has been reported from Canada (British Columbia 
to Quebec) and as far south as Argentina. In addition to Canada 
and the United States human cases have been reported from Mexico, 
the Caribbean, Panama, French Guiana and Argentina (Tsai and 
Mitchell, in press). There are apparently two epidemiological 
cycles. One predominately in the western United States has been 
rural and involved Culex tarsalis as the primary vector. The 
other in the east is primarily urban with Culex pipiens being the 
major vector. With increasing urbanization in the western United 
States there are indications that outbreaks in western cities, 
(e.g. Los Angeles in 1984) may be more like the urban cycle of SLE 
in the east (CDC 1985) . 

Natural infections of SLE virus are pathogenic only to 
humans (Tsai and Mitchell 1986). Hamsters, mice, suckling rats 
and rhesus monkeys are susceptible by cranial injection (Natharson 
1980) . Birds are considered the most important group of hosts 
with species from 13 avian families identified serologically as 
potential hosts (McLean and Bowen 1980) . Numerous species of 
rodents, ungulates and cricetids have also been identified as 
potential hosts (McLean and Bowen 1980) . Several species of bats 
(Myotis lucifugus , Eptesicus fuscus) in the central United States 
have been shown to exhibit high seroactivity (Herbold et al. 
1983). Virus has been isolated from hibernating bats in Texas, 



24 



and may be a possible overwintering mechanism for the virus (Allen 
et al. 1970). 

iii. Clinical Aspects 

SLE virus is pathogenic only to humans by natural 
infection. Most humans infected are asymptomatic. Approximately 
200-300 asymptomatic infections occur for each symptomatic case 
(Monath 1980). Of ca. 4,000 individual sera examined during the 
1975 outbreak in southwestern Ontario, approximately 0.83% were 
positive (Artsob et al. 1979). Assuming a population base of ca. 
500,000 individuals in this region, ca. 4,000 individuals were 
infected with SLE virus. From this infected group 66 clinical 
cases of SLE were identified, of which five were fatal (Joshua 
1979). This fatality rate of 7.6% was similar to that of 8% found 
in Chicago during the 1975 outbreak (Zweighaft et al . 1979). 

In Ontario, 36 female and 30 male patients were reported, 
with no sexual bias for the disease. All age groups were affected 
but cases were more common in individuals over 19 years of age 
(56/66). Mortality occurred in individuals 45 or over. These 
cases agree with the United States data where case fatality ratios 
vary from 5-20% with high ratios occurring in older patients 
(Monath 1980) . 

In Ontario, cases were placed in one of four categories: 
1) mild influenza - no sequelae (4.5%), 2) mild meningeal 
involvement (photophobia, insommia) with excessive fatigue and 
mild depression as sequelae (36.4%), 3) increased meningo 
encephalitis, neck stiffness, marked photophobia, disorientation 
with long sequelae marked by excessive fatigue, weakness and acute 
depression (51.5%), and 4) coma and death (7.6%). Six months 
after infection 31 patients had completely recovered and 34 had 
some sequelae (Joshua 1979) . The most common symptoms were fever 
89%, headache 74%, stiff neck 57%, vomiting 56% and general 
malaise 48%. Disorientation was observed in 45% of the cases, 
coma in 10% and convulsions in 3% (Joshua 1979) . 

Of the described mortalities in Ontario during 1975 the 
patients (3) had coexisting disease Draisey et al. (1979). In 
fatal cases abnormalities are confined to the central nervous 
system (Suzuki and Phillips 1966) . The meninges and spinal cord 
are infiltrated with macrophages, lymphocytes and occasionally 
polymorphonuclear cells. Microglial proliferation can be seen 
around dead and dying neurones (neuronophagia) and may be diffuse 
or focal in the white matter (Draisey et al. 1979). . 

In summary, the clinical aspects of SLE in patients from 
southern Ontario during 1975 were consistent with previous 
outbreaks and the concurrent outbreak of SLE in the United States. 
This reinforces the concept that SLE in eastern Canada and 
probably in western Canada are northern extensions of the United 
States epidemics. 

iv. Epidemiology 

St. Louis Encephalitis is primarily a disease of 
passeriform and columbiform birds and is transmitted by mosquitoes 

25 



(Monath 1980) . Humans are only incidentally involved with most 
cases occurring in August and September. In Ontario, in 1975, the 
first confirmed case of SLE occurred during 27 July - 3 August, 
and the last case on 27 September (Jones 1979). The majority of 
cases occurred during the last two weeks of August and the first 
two weeks of September. The majority of cases in the Windsor area 
were from within the city limited (37) with 13 cases in rural 
areas. This is a reflection of the population distribution of 
residents of the region rather than case prevalence in the city. 

There are two recognized cylces of SLE transmission in 
northern latitudes. The rural or western cycle involves Culex 
tarsalis as the primary vector and is considered rural in nature. 
The second involves Culex pipiens as the vector and is considered 
urban in nature. Culex tarsalis breeds in clear to polluted water 
in stagnant fresh water habitats. Culex pipiens by contrast 
occurs primarily in polluted waters, e.g. catch basins and sewage 
lagoons. Adults are abundant in urban situations. Culex restuans 
is also prevalent in urban environments and may transmit SLE 
virus. The life history and population dynamics of C. pipiens and 
C. restuans have been detailed in Ontario (Madder et al. 1983b). 
Culex pipiens has been incriminated as the most probable vector of 
SLE in Ontario with two virus isolations (Thorsen et al . 1980) 
Other mosquito species of Canada which have been shown 
experimentally to transmit SLE virus are Aedes sticticus , Aedes 
vexans and Culiseta inornata (Chamberlain et al. 1959). In 
widespread epizootics transmission to humans may occur. SLE virus 
has also been isolated from other mosquito species in the United 
States, mites and a tick (Mitchell et al. 1980). 

The overwintering mechanism of SLE virus is equivocal. SLE 
virus has been isolated from overwintering Culex pipiens females 
in Maryland and Pennsylvania (Bailey et al. 1978). Transovarial 
transmission of the virus occurs experimentally (Francy et al. 
1981) but infection rates are low and may not be significant in 
nature. The virus may overwinter in birds (Chamberlain et al. 
1957) or bats (Sulkin and Allen 1974) . Other mechanisms may occur 
(Reeves 1974) . 

In Ontario, it would appear that the virus successfully 
overwintered (mechanism unknown) during the winter of 1975-76. 
There was no evidence of virus activity in sentinel chickens , 
English sparrows or mosquito pools during five years of subsequent 
monitoring in Ontario (1977-1983). One can assume that the virus 
is not endemic to the Province of Ontario. The virus potentially 
can be moved long distances by infected migratory birds or 
infected mosquitoes being dispersed from the southern United 
States to Canada on weather fronts. 

c. Eastern Equine Encephalitis (EEE) 

. History and Nature 

EEE has been known in North America for a long time. In 
1831 a fatal neurologic disease was first described in horses 
along the east coast of the United States in Massachusetts. The 

26 



virus was first isolated from horses during an outbreak in 
Maryland in 1931. In 1938 the virus was located from a human in 
Massachusetts. Subsequently the virus has been recovered during 
outbreaks from as far west as South Dakota, Wisconsin, Michigan 
and Indiana, along the eastern Atlantic and Gulf coasts in the 
U.S., throughout the Caribbean area and Central America and in 
South America. In Canada, the virus has been isolated from a 
horse and a migrating Junco in 1938 and 1961, respectively, in 
Ontario; from snowshoe hare in Alberta in 1962 and from horses in 
Quebec in 1972. The virus has never been isolated outside the 
western hemisphere. 

The EEE virus is an arbovirus belonging to the family 
Togaviridae. There are two antigenic variants having distinct 
geographical distribution and characterized as North American and 
South American types. The latter appears to be more antigenically 
heterogenous than the former. 

ii. Clinical 

EEE clinically affects man, horses and certain species of 
birds. The early names of equine sleeping sickness, forage 
poisoning and blind staggers by which EEE was known are simply 
clinical manifestations of the disease in horses. In horses an 
initial fever of 40.5 C develops 1 1/2 days after infection and 
persists for about a day. At this stage clinical signs are 
anorexia and depression. A second febrile response occurs 4 to 6 
days after infection with a temperature of 39.5 to 40 C which 
persists for 1 to 4 days. During this second stage, neurologic 
signs develop including profound depression characterized by a 
wide stance, hanging of the head, drooping of the ears, flaccid 
lips and difficulty in swallowing. Foetid breath, diarrhea or 
constipation, and a dramatic weight loss of 50 to 100 kg are 
frequent. Some animals become restless, excitable, incoordinated, 
unsteady, hyperesthetic, walk in circles and into obstacles, press 
the head against obstacles, appear blind and deaf, grind their 
teeth, chew aimlessly and itch intensely with the removal of large 
patches of hair by chewing or scratching. Eventually the affected 
animals became weak, fall down and die within 5 to 10 days. 
Horses that recover may have cerebral dysfunction although many 
appear normal . 

In man, and especially in children, the disease is 
fulminating, with high fever, lethargy, vomiting, convulsions and 
the patient is gravely ill within 2 days of onset. Other signs 
include nuchal rigidity and coma. Mortality rates often exceed 
65% among clinically ill persons. Survivors are frequently 
affected by neurologic and physical sequelae that include 
retardation, hemiparesis, aphasia, emotional instability, 
convulsions, hemiplegia, strabismus, impaired vision, partial 
deafness and speech disorders. 

EEE infections produce high viremias of several days 
duration in birds but except for certain domesticated fowl, 
pigeons and pheasants, causes low mortality. 



27 



iii. Epidemiology 

The normal transmission of EEE virus is via mosquitoes to 
wild rodents or wild and domestic birds. Man and horses are 
tangentially infected, with low to moderate viremia and although 
horses are probably dead-end hosts under most circumstances, the 
level of viremia is sufficient to infect the more efficient 
mosquito vectors. The female mosquito becomes infected after it 
takes a virus -infected blood meal. The virus replicates in the 
midgut cells , passes to the coelomic cavity and haemolymph and 
infects nearly all organs and tissues. The virus also replicates 
in salivary glands and probably persists there for the life of the 
insect. Most mosquitoes that act as biological vectors can 
transmit virus 10 days after initial ingestion of the infective 
blood meal. 

In the endemic cycle, EEE virus is transmitted among birds 
in fresh water swamps. The principle vector appears to be 
CuliseCa melanura, a swamp breeding mosquito that is 
preferentially a bird- feeding species. Epidemics of EEE in horses 
and man have generally originated in the vicinity of swamps, 
although these hosts are not infected within the swampy endemic 
focus. Outbreaks often occur after hot excessively rainy weather. 
When virus infection rates in birds are high, other mosquitoes, 
possibly floodwater species probably transmit the virus to horses, 
man and pheasants. Aedes sollicitans (a salt marsh mosquito), 
Psorophora confinnis (a fresh water species that breeds in 
temporary rain pools), Culiseta morsitans , the Culex pipiens- 
restuans complex, Aedes vexans and Ae. canadensis have either been 
associated with EEE epidemics or have been suggested as vectors. 

The mechanism of EEE virus overwintering is unknown. 
Despite the movement of both serotypes of EEE virus in migrating 
birds, there is no evidence to support annual reintroduction of 
the virus rather than the existence of stationary foci of 
infection. A proposed mechanism would involve recrudescence of 
EEE virus from reservoir hosts. Isolations of EEE virus from 
cats , dogs , mice , foxes and a skunk during winter are evidence for 
the possibility of an overwinter cycle involving one or more of 
these species even though birds are more likely permanent 
reservoir hosts. There are also experimental infections and 
naturally occurring antibody in reptiles and amphibians; these 
species could also be overwintering hosts. 

In Canada the fact that EEE virus has only been isolated 
occasionally from widely separated geographic areas over many 
years and does not appear to have become permanently established 
is evidence that virus is either introduced via a viremic host or 
infected mosquitoes are brought into an area via unusual air 
currents to establish a transitory focus of infection. 



28 



3. VECTORS 

a. Known and Potential Vectors of Western Equine Encephalitis 
i. Survey of Viral Isolations 

Western Equine Encephalitis (WEE) has been isolated most 
frequently from Culex tar sal is , the primary vector in both Canada 
and the United States (Hess and Hayes 1967; McLintock and Iversen 
1975; Sekla and Stackiw 1982; Sekla et al . 1980; Reeves and Hammon 
1962) . In Saskatchewan, 9 isolations of WEE virus were made from 
Cx. tarsalis in 1963 and 10 in 1965 (McLintock et al. 1970). The 
seasonal infection rates were 1:145 and 1:169 Cx. tarsalis , 
respectively. In Manitoba, 33 isolations of WEE virus were made 
from Cx. tarsalis in 1977 and 18 in 1981; the Cx. tarsalis 
seasonal infection rates were 1:347 in 1977 and 1:283 in 1981 
(Sekla and Stackiw 1982) . WEE virus was isolated from mosquitoes 
in 1975, an epidemic year in Manitoba, but those mosquitoes were 
not identified to species (Sekla et al. 1980). Cx. tarsalis was 
abundant in Winnipeg that year (Brust and Ellis 1976a) and 5 out 
of 14 human cases were from this urban area (Waters 1976) . This 
indirectly implicates Cx. tarsalis as the vector in 1975 in 
Manitoba. 

Isolations of WEE virus have been made from naturally 
infected Culiseta inornata, Cx. restuans , Cx. pipiens complex , 
Cx. peus , Mansonia (-Coquillettidia) perturbans , Anopheles earlei 
and several Aedes species from Canada and the United States 
(Hammon et al. 1945; McLintock et al. 1970; Norris 1946; Reeves 
and Hammon 1962; Sekla et al. 1980). In some cases the rate of 
infection has been higher in these secondary vectors than in Cx. 
tarsalis . The rate of infection in An. earlei and Ma. perturbans 
in Manitoba during 1977 was 1:87 An. earlei and 1:202 Ma. 
perturbans respectively, compared to 1:347 Cx. tarsalis (Sekla et 
al. 1980). However, these isolations were made from a waterfowl 
nesting area and are not representative of agricultural or urban 
regions of the Province. Also, populations of these species do 
not occur in high density in Manitoba, with the exception of Ma. 
perturbans in a few marsh habitats. Ma. perturbans adult activity 
is only 3-4 weeks in length. Thus this species is an unlikely 
vector of WEE virus to equines or humans but may be involved in 
the amplification of the virus in the bird-mosquito-bird cycle. 

In Alberta, WEE virus was isolated from Aedes vexans , Cs . 
inornata, and Cx. tarsalis (Shemanchuk and Morgante 1968) during a 
non-epidemic year. Cx. tarsalis is known to be abundant in 
southern Alberta (Shemanchuk 1969) and was the most likely vector 
during the 1963 epidemic and the 1964 epizootic of WEE in that 
Province . 

In Manitoba, natural infections of WEE virus were found in 
Ae. vexans, Cs. inornata and Ae. pionips . However, the infection 
rates were considerably lower than in Cx. tarsalis (Sekla et al. 
1980) . Although many species can transmit WEE virus 
experimentally (Ferguson 1954) , it is not known if their natural 
populations are competent vectors of the virus. 

In Saskatchewan, WEE virus was isolated from Cs . inornata 11 

29 



times during 1963-1965. The infection rate was only 1:4664 Cs . 
inornata in 1963, 1:1209 in 1964 and 1:2416 in 1965, about 1/20 
the rate for Cx. tarsalis during those years (McLintock et al . 
1970). Isolations were also made from Ae. vexans , Ae. dorsal is , 
Ae . campesCris , Ae. flavescens and Ae. spencer ii. However, the 
number of isolations ranged from 1 to 3 per species over a 3 year 
period. The finding that most of the WEE virus isolations in 
Aedes spp . were made during an inter-epidemic year in Saskatchewan 
led McLintock et al. (1970) to suggest that Aedes spp. and Cs . 
inornata may maintain the enzootic status of the virus in that 
Province. Aedes spp. and Cs . inornata may also be the primary 
vectors of WEE virus in the Northwest Territories (N.W.T.) where 8 
out of 160 reindeer, Rangifer spp. , were found to have WEE 
antibodies (Burton and McLintock 1970) . Cx. tarsalis has been 
collected only once from the N.W.T. (Wood et al. 1979), and is 
generally not found at those latitudes. 

In the United States, WEE virus has been isolated from Aedes 
trivittatus from Iowa (Rowley et al. 1979) and Ae. melanimon from 
California (Hardy and Bruen 1974) . Aedes melanimon is associated 
with the endemic WEE cycle in jack rabbits, but the role of Ae. 
trivittatus in the natural transmission of WEE virus is unknown. 

The status of Cx. restuans as a vector of WEE virus in 
N.A.is yet to be established. In Manitoba, this species is known 
to be abundant because of the numerous egg rafts collected from 
oviposition pools (Buth 1983) , but very few adults are attracted 
to C0 2 traps or to light traps (Brust and Ellis 1976a; Gallaway 
1983) . Because so few females have been tested for WEE virus in 
Manitoba, it is not surprising that only 1 isolation has been 
reported (Norris 1946) . It is active much earlier in the summer 
than Cx. tarsalis (Brust and Ellis 1976a) , and may be involved in 
a bird-mosquito-bird cycle. Recently, Monath (1984) has suggested 
that Cx. restuans may be involved in the spring amplification of 
St. Louis Encephalitis (SLE) virus in the Memphis, Tennessee area. 
Infection levels were higher in Cx. restuans than in the Cx. 
pipiens complex during the spring and fall of the non- epidemic 
year of 1979. 

The primary vectors of SLE virus in the United States are 
Cx. p. pipiens in the eastern and the northern states, Cx. p. 
quinquefasciatus in the southern and southeastern states (up to 39 
NL) , Cx. nigripalpus in Florida, and Cx. tarsalis in the western 
states (Mitchell et al. 1980). These are responsible for epidemic 
virus transmission to humans and for the enzootic virus 
transmission amongst wild vertebrates. During non-epidemic years, 
where the ranges of Cx. pipiens complex and Cx. tarsalis overlap, 
SLE virus is isolated more frequently from the latter species 
(Mitchell et al. 1980). In the eastern states, Cx. restuans and 
Cx. salinarius may play an important role in the sylvan enzootic 
transmission of SLE (Monath 1980, 1984). 

SLE virus has been isolated from Cx. tarsalis in 
Saskatchewan (Burton et al. 1973), and from Culex spp, mostly Cx. 
pipiens, from Ontario (Thorsen et al. 1979). 

In the eastern and southern United States, isolation of SLE 

30 



virus from the Cx. pipiens complex during 1974-1976 demonstrated 
an infection rate of 1:178 Cx. pipiens (Monath 1979). In 
Illinois, Kokernot et al. (1967) reported an infection rate of 
1:51. Isolations of SLE virus from Cx. salinarius have been as 
high as 1:74 Cx. salinarius in the southern and eastern States, 
and as high as 1:73 in Memphis, Tennessee, during 1974-1976 
(Monath 1979). 

The list of natural and experimental vectors of SLE virus 
will undoubtedly continue to grow. The mosquito vectors known to 
date and a discussion of their significance in the SLE cycle in 
the United States can be found in Mitchell et al. (1980). 

ii. Virus Amplification 

The spring amplification phase of WEE and SLE viruses in 
North America begins with these viruses being present in either 
the mosquito vectors or wild bird reservoirs. Wild birds sustain 
inapparent infections with viremias sufficient for infection of 
mosquitoes in the well known bird-mosquito-cycle. The mechanism 
whereby these viruses overwinter or are re -introduced in the 
spring is unknown (Hess and Hayes 1967; Monath 1979, 1980). 

In the spring and early summer the mosquito vectors of both 
WEE and SLE feed on avian hosts. Cx. tarsalis and Cx. nigripalpus 
significantly shift their preference from avian to mammalian hosts 
in mid-summer (Edman and Taylor 1968; Hayes et al. 1973; Tempelis 
1975; Tempelis et al. 1965; Tempelis and Washino 1967). This 
shift is an important phenomenon in mosquitoes obtaining these 
viruses from the avian reservoir and transmitting them to humans 
(Edman and Taylor 1968; Reeves 1971). Passerine birds are 
preferred hosts of C. tarsalis in California and Texas, and 
nestlings serve as the primary amplification host( Hayes et al. 
1961; Reeves and Hammon 1962). The factors that determine the 
rate of amplification are the numbers of infected and infective 
mosquito vectors (Hess and Hayes 1967; Reeves 1965; Reeves et al. 
1961). 

ill. Transmission 

Transmission of viruses, including WEE and SLE, has been 
reviewed by Chamberlain and Sudia (1961). This section deals with 
WEE and SLE transmission by the primary vectors and the factors 
that affect the successful transmission of these viruses. 

Vector abundance is one of the more important factors in the 
successful transmission of both WEE and SLE viruses to humans 
(Reeves 1965). Epidemics of WEE and SLE are correlated with high 
levels of vector abundance (Brust 1982; Hess and Hayes 1967; 
McLintock et al. 1966; Mitchell et al. 1980; Olson et al. 1979; 
Rees et al. 1959; Reeves and Hammon 1962). However high vector 
populations have been present during years in which epidemic 
spread did not occur (Reeves et al. 1964). Vector abundance in 
Winnipeg, Manitoba was also greater during the non- epidemic years 
of 1978 and 1984 than during the epidemic year of 1981 (Raddatz 
1985). 

Extrinsic incubation temperature (body temperature of the 

31 



vector) is another important factor in the transmission of WEE and 
SLE viruses to vertebrates (Hess et al . 1963; Reeves 1965; Reeves 
et al. 1964). After acquiring an infective blood-meal, Cx. 
tarsalis incubates WEE or SLE virus for several days before being 
able to biologically transmit the virus to a new host. The 
temperature of extrinsic incubation in the vector may be the 
reason WEE outbreaks have occurred at or above the 21 C June 
isotherm whereas SLE outbreaks have occurred at or below the 21 C 
isotherm (Hess et al. 1963). 

WEE and SLE virus transmission varies with vector efficiency 
(competence) of the particular strain of vector (Reeves 1965) . 
Vector competence and its role in virus transmission has been an 
active topic in recent years, and a number of reviews are 
available ( Gubler et al. 1982; Hardy et al. 1983; McLintock 1978; 
Mitchell 1983a) . These should be consulted for details on 
Salivary Gland Infection (SGI) Barrier, Mesenteronal Infection 
(MI) Barrier, Mesenteronal Escape (ME) Barrier and leaky midgut. 
A recent study has shown that the MI barrier to WEE virus in Cx. 
p. pipiens may be due to the failure of the virus to penetrate the 
gut epithelium (Houk et al. 1986). 

The virus dose acquired by a vector plays a role in the 
successful transmission to another host. In a Manitoba strain of 
Cx. tarsalis , infected with a WEE virus isolate from Manitoba, the 
infection threshold in 50% of Cx. tarsalis , infected via a blood- 
meal from a viremic chick, was log 2.3 Tissue Culture Infective 
(50% level) Dose (TCID50) per 0.3 ml of donor blood. Transmission 
rates were near 100% after 25 days (Henderson et al. 1979). 
Biological transmission of WEE virus by Cx. tarsalis , has been 
shown to be a minimum of 4 days at 24 C when transmitted from 
chick to chick or chick to mouse (Henderson et al. 1979; Hayles et 
al. 1972; Hayles 1976). From chick to mouse, Henderson et 
al. (1979) obtained 76% transmission. From chick to chick 81% 
transmission occurred over 31 days. Hayles et al. (1972) obtained 
86% transmission from chick to chick over 44 days. 

Biological transmission of SLE virus in 100% of infected Cx. 
p. pipiens may be reached after 12 days of extrinsic incubation, 
whereas transmission rates of only 18 to 29% occurred in Cx. p. 
quinquefasciatus after a comparable incubation period. 
Transmission rates in the latter subspecies reached 100% after 19 
to 26 days of extrinsic incubation (Chamberlain et al. 1959). 

Strains of Cx. tarsalis which are highly resistant to WEE 
virus infection have been isolated after prolonged selection. 
Resistance has been associated with a mesenteronal barrier, 
because both refractory and parental strains were equally 
susceptible to infection by intrathoracic injection. Inheritance 
of WEE virus susceptibility is probably polyfactorial in Cx. 
tarsalis (Hardy et al. 1978). Genetic selection in laboratory 
populations and seasonal variations amongst field populations of 
Cx. tarsalis have also been shown to affect the infection and 
transmission rates of WEE virus (Hardy et al. 1979). 

Transovarial transmission of SLE virus by Cx. pipiens 
complex mosquitoes (Francy et al. 1981; Hardy et al. 1984) and by 

32 



Cx. tarsalis , Ae. epacCius , and Ae . atropalpus (Hardy et al. 1984) 
has been demonstrated experimentally. Francy et al. (1981) 
obtained low transmission rates in progeny from the first ovarian 
cycle, but the transmission rates increased as much as 30 fold in 
the second cycle. Hardy et al. (1984) obtained much higher rates 
of infection in progeny from the first ovarian cycle in the 
species they tested, including laboratory populations of Cx. 
pipiens and Cx. tarsalis . In both studies low temperature 
maintenance (18°C) of larvae and adults was necessary to obtain 
successful transmission to Fl larval or adult progeny (Francy et 
al. 1981 and Hardy et al. 1984). 

iv. Overwintering of Vectors 

Females of Cx. tarsalis and Cx. p. pipiens overwinter as 
inseminated, nulliparous females (Bellamy and Reeves 1963; 
Bennington et al . 1958b; Blackmore and Dow 1962; Spielman and Wong 
1973a) . Low temperature and short photoperiod induce a 
facultative ovarian diapause. Females seek nectar rather than a 
blood-meal to build fat body reserves for overwintering (Eldridge 
1968; Eldridge and Bailey 1979; Harwood and Halfhill 1964; 
Mitchell 1981,1983a; Spielman 1971a; Wilton and Smith 1985). The 
life stages sensitive to these induction cues are fourth instar 
larvae and pupae (Eldridge 1968; Reisen 1986, Reisen et al . 1986b; 
Spielman and Wong 1973a, b). In southern Ontario initiation of 
diapause begins in late July, with 90% of emerging adults being in 
diapause in mid-August (Madder et al. 1983a). If vector control 
was necessary to halt an epidemic in progress, larviciding to 
control Cx. p. pipiens in Ontario would not affect transmission 
after mid- August. Over 90% of the newly emerged females would not 
be involved in blood- feeding and therefore would be unable to 
transmit a pathogen. 

Diapausing females of Cx. p. pipiens and Cx. tarsalis can be 
induced to take a blood-meal if they are warmed to 25 C for 1 to 
3 days and placed in close association with a suitable host 
(Eldridge and Bailey 1979; Mitchell 1981, 1983b). However, 
diapause is not terminated under these conditions. The females 
are induced to blood-feed by avoiding the host-seeking step in the 
biting cycle. If diapausing females are placed in a 3.8 L 
container for blood- feeding instead of a 0.24 L one, adding host- 
seeking to the feeding cycle, the females do not feed (Mitchell 
1981,1983b). Some diapausing females of Cx. p. pipiens and Cx. 
tarsalis that blood- feed, when placed in close association with 
the host, fail to use the blood for egg development. This 
occurred when females were kept at 15 C and a short photophase for 
1 week (Arntfield et al. 1982; Eldridge and Bailey 1979; Mitchell 
1981, 1983b). However, this probably has little significance to 
what occurs in nature because diapausing females would not be in 
the host- seeking mode and would not take a blood-meal. 

Fat body size in Cx. tarsalis increases after females take a 
carbohydrate meal. In nature, females have significant lipid 
reserves in the fall and winter months (Bennington et al. 1958b; 
Schaefer and Washino 1969, 1970; Takata and Harwood 1964). 

33 



Females of Cx. p. pipiens also develop considerable fat reserves 
on a carbohydrate diet when maintained at 5 C (Tekle 1960) but 
less than prehibernating Cx. p. pipiens in nature (Eldridge 1968). 
When females of Cx. p. pipiens are kept at a short photoperiod at 
10 C, considerably more fat reserves are accumulated than in Cx. 
p. quinquefasciatus (Eldridge 1968). 

Females of Cx. tarsalis in nature become increasingly cold 
tolerant as fall progresses to winter (Anderson and Harwood 1966) . 
Adults collected in October in Washington State survived longer at 
low temperatures than did adults collected in August. Females 
have been shown to accumulate a larger percentage of unsaturated 
fatty acids in their fat body in response to low temperatures and 
short photoperiods . This accumulation may provide the increased 
cold tolerance (Harwood and Tanaka 1965) . 

Overwintering sites for Cx. tarsalis in Canada are largely 
unknown. Shemanchuk (1965) found that overwintering adult females 
survived in badger, skunk and marmot burrows in southern Alberta. 
Hudson (1978) found several species of mosquitoes overwintering in 
rock piles, root cellars and badger burrows in central Alberta. 
However no overwintering females of Cx. tarsalis were found during 
the 3 winters (November to March) in which numerous adults of An. 
earlei (445) and Cx. territans (106) were found. 

In the western United States, overwintering females of Cx. 
tarsalis have been found in abandoned mines (Blackmore and Winn 
1956; Chapman 1961; Mitchell 1979), outdoor food storage cellars 
(Keener 1952) , under loose rock on canyon and cliff slopes 
(Harwood 1962; Rush 1962), under bridges (Dow et al. 1976), inside 
culverts (Kliewer et al. 1969) and in rodent burrows (Bennington 
et al. 1958b). 

The spring emergence of Cx. tarsalis from natural 
overwintering sites is correlated with the time of the spring 
inversion of soil temperatures (Bennington et al. 1958a; Dow et 
al. 1976; Shemanchuk 1965). In southern Alberta Cx. tarsalis 
emerged from animal burrows in April and May (Shemanchuk 1965). 

b. Known and Potential Vectors of Eastern Encephalitis Virus 

There have been numerous isolations of EEE virus and 
antibodies in a variety of birds and mammals in Canada (Artsob and 
Spence 1979) , yet no infected mosquitoes have been identified to 
date in this country. In the United States, Culiseta melanura 
appears to be the primary enzootic vector (Chamberlain 1987) . 
Female Cs . melanura are predominately ornithophilic (Hayes 1961; 
LeDuc et al. 1972) and circulate EEE virus among avian hosts in 
swamplands and margins in endemic areas (Grimstad 1983; Howard et 
al. 1983). Culiseta melanura overwinters in the larval stage and 
is restricted in its distribution in Canada to extreme eastern 
Ontario and southern Quebec (Chant et al. 1973; Ellis and Wood 
1974; Wood et al. 1979). It is, therefore, unlikely that Cs. 
melanura constitutes a primary role in EEE virus transmission in 
Canada, unless there are isolated pockets of infection among 
resident birds which are so far undetected. 

Eastern equine encephalitis virus has been isolated from 

34 



many additional genera and species of mosquitoes, some of which 
are probably responsible for virus transmission to mammals, 
including horses and man. Hansonia perCurbans , a widely 
distributed and viscious biter in Canada, was first identified as 
a vector for EEE virus by Howitt et al . (1949). Since then, it 
has been suggested repeatedly as an important vector in the spread 
of EEE virus out of marshland areas and to mammal hosts (Srihongse 
et al. 1980; Grimstad 1983). Aedes solliciCans and Ae. 
taeniorhynchus have been implicated as important vectors in the 
eastern saltmarshes of the United States (Crans 1977) . Because of 
the restricted distribution of the former (Wood et al. 1979), and 
absence of the latter in Canada, they are undoubtedly of no 
consequence here. Aedes vexans , Ae. canadensis , and Ae. cantator , 
all of which occur more widely in Canada (Wood et al. 1979), have 
been suggested as possible vectors of EEE virus (Grimstad 1983) . 
Infected Culex restuans , Cx. pip Lens and Cs. morsitans have been 
recovered in New York (Srihongse et al . 1980), but their role in 
the epidemiology of EEE is unknown. 

In Canada, therefore the primary vector candidates for EEE 
virus are tiansonia perturbans and perhaps Aedes spp. Although 
Culiseta melanura is present in eastern Canada, it is rare and 
limited in distribution. It is possible, however, that low levels 
of virus may be circulated among bird populations where Cs . 
melanura does occur, and an alternate vector is then responsible 
for transmission to mammal hosts. Vectors responsible for exposed 
animals in Alberta and Saskatchewan (Artsob and Spence 1979) are a 
matter of conjecture, but Ma. perturbans would be an interesting 
species to examine in more detail. 

c. Known and Potential Vectors of California -group Viruses 
California encephalitis virus 

California encephalitis virus is reported to cause human 
illness (Hammon and Reeves 1952) , but only three cases have been 
identified in North America (California) (Monath 1979). This 
virus is widespread in the United States, having been reported 
from California, Utah, New Mexico and Texas (Calisher 1983). This 
virus has only recently been isolated from Canada, from a pool of 
Culiseta inomata collected from Selkirk/Oak Hammock, Manitoba 
(Artsob et al. 1985). California encephalitis virus is generally 
believed to be transmitted by Aedes spp. (Le Due 1979), including 
Ae. dorsalis , Ae. melanimon, Ae. nigromaculis and Ae. vexans 
(Turell and LeDuc 1983). However, isolations have also been made 
from Culex tarsalis , Anopheles freebomi, and Psorophora 
signipennis , as well as Cs . inomata in the United States. It is 
interesting that in laboratory trials conducted by Reeves and 
Hammon (1952), Cx. tarsalis and Cs . inomata were unable to 
transmit California encephalitis virus after feeding on an 
infected blood source. 

All species of mosquitoes from which California encephalitis 
virus has been isolated in the field, occur in Canada (Wood et al. 
1979). Some of these, such as Ae. vexans, Ae. dorsalis , Cs . 
inomata and Cs . tarsalis are widespread, often abundant, and 

35 



known to bite man. However, the prevalence of California 
encephalitis virus is very low, and considering the rarity of 
human cases, does not deserve primary concern in Canada at the 
present time. 

Snowshoe Hare virus 

Snowshoe Hare virus has been implicated in the cause of 
human disease (Feltz et al. 1972; Lindsey et al. 1976), and has 
been isolated from all provinces and territories in Canada (Artsob 
1983) . Most isolations from mosquitoes have been recovered from 
Aedes spp. , especially the univoltine species predominant in the 
boreal, subarctic and arctic regions where Snowshoe Hare virus is 
endemic (LeDuc 1979) . A summary of naturally infected vector 
species was provided by LeDuc (1979), and includes Aedes 
canadensis , Ae. cataphylla, Ae. cinereus , Ae. communis, Ae. 
excrucians , Ae. fitchii, Ae. hexodontus , Ae . implicaCus , Ae . 
intrudens , Ae. punctor and Ae. vexans . Only the latter, Ae. 
vexans , is multivoltine, and of these has been shown to become 
infected and to transmit the virus in the laboratory (LeDuc 1979) . 
Turell and LeDuc (1983) included Ae. sCimulans , Ae. triseriatus , 
and Ae. trivittatus among additional sources for virus isolations. 
Culiseta inornata may also be an important vector in more southern 
latitudes. Morgante and Shemanchuk (1967) discovered Snowshoe 
Hare virus in adult Cs . inornata collected from mammal burrows in 
southern Alberta. McLean et al. 1974 demonstrated the ability of 
Cs. inornata to acquire and transmit the virus in the lab, and for 
the virus to persist for prolonged periods of time within these 
mosquitoes at low temperature (McLean et al. 1975, a,b). Snowshoe 
Hare virus has also been isolated from the black fly, Simulium 
malyschevi in Alaska (Ritter and Feltz 1974) , but its role as a 
vector for the virus is unknown. 

Aedes species are generally believed to be the primary 
vectors of Snowshoe Hare virus over most of its range. In some 
areas, however, Cs. inornata clearly may play an important role in 
maintenance and transmission of the virus. More research is 
needed to illucidate the relative importance of the various vector 
species present in endemic areas . 

Jamestown Canyon virus 

Jamestown Canyon has been implicated in human disease in 
Canada from a single isolation in Ontario (Deibel et al. 1983). 
Virus isolations over most of the known range from Aedes spp., 
including Aedes cantator , Ae. communis, Ae. melanimon, Ae. 
punctor, Ae. sollicitans , Ae. stimulans , Ae. thelcter , Ae. 
trivittatus , and Ae. vexans, but Anopheles crucians , An. 
punctipennis , An. quadr imaculatus , Psorophora columbiae, and Ps. 
discolor have also provided sources of isolations (Turell and 
LeDuc 1983). However, in the western United States, Culiseta 
inornata has been the major source of isolation in the field, and 
is known to transmit the virus in the laboratory (Turell and LeDuc 
1983) . Isolations of James twon Canyon virus are also known for 
the tabanids, Chrysops cincticornis , Hybomitra lasiophthalma and 

36 



H. nuda (Turell and LeDuc 1983), though their role in virus 
dissemination is unknown. 

Virus isolations and positive antibody determinations for 
Jamestown Canyon virus are widespread in Canada (Hoff et al. 1969; 
Iversen et al. 1973; MacFarlane et al. 1981, 1982; Artsob 1983). 
Since many of the mosquitoes from which this virus has been 
isolated occur and may be widespread in Canada, the potential for 
additional human clinical cases is clearly present. 

Trivittatus virus 

Trivittatus virus is suspected as causing human disease 
(LeDuc 1979) , but there is no available evidence to support this 
in Canada. There is, in fact, only one isolation of this virus 
from mosquitoes (Aedes trivittatus) from extreme southwestern 
Ontario (Thorsen et al. 1980). There have been no other virus 
isolations or seropositive vertebrates reported for Canada (Artsob 
1983). The low prevalence of Trivittatus virus might be expected, 
considering that Aedes trivittatus , which is probably the 
principal vector for the virus in the United States, is quite 
restricted in Canada (Wood et al. 1979). Nonetheless, Trivittatus 
virus has been isolated from many other mosquito species in the 
U.S., including Aedes at lanticus/ tormentor , Ae . dorsalis , Ae. 
infirmatus , Ae. sollicitans , Ae. taeniorhynchus , Ae. triseriatus , 
Ae . vexans , Anopheles crucians , Mansonia perturbans , Culex 
nigripalpus , Cx. pipiens , Culiseta inomata, and Psorophora 
signipennis (Turell and LeDuc 1983) . 

Many of the California group viruses have been isolated in 
the field from a large number of blood- feeding arthropods. For 
example, Snowshoe Hare, Jamestown Canyon, and Trivittatus viruses 
have been recovered from 20, 18, and 14 species respectively. 
However, in all cases, the number of vectors that are in fact 
important in the spread of the virus from one vertebrate host to 
another is limited. Because of the blood- feeding habit, it is 
conceivably quite easy for an arthropod to acquire virus from a 
suitable viremic host. Other factors, including the 
morphological, physiological and behavioural characteristics of 
the arthropod, however, influence the competency of the arthropod 
to transmit the virus upon subsequent blood meals. It takes a 
considerable amount of time and research effort before these 
levels of competency can be established, and it is in this area 
that our knowledge of the status of the California group viruses 
is greatly deficient in Canada. 

d. Possible Overwintering of Viruses 

In Canada, endemic foci of mosquito -borne viruses can 
persist only where suitable mechanisms for winter survival are 
available and highly successful. Unfortunately, the amount of 
information on overwintering of these viruses is sadly lacking. 

There are essentially three possible mechanisms by which 
viruses may be maintained in invertebrate vector populations , as 
described by Reeves (1974). Viruses may survive within the 
primary mosquito vector populations where long-lived adults obtain 

37 



a viremic blood-meal before entering hibernation, and then retain 
the infection through hibernation, to transmit the virus with the 
first blood-meal(s) in the spring. On the other hand, primary 
mosquito hosts may transmit the virus transovarially , and maintain 
infected vectors in the population even in the absence of 
suitable, viremic vertebrate hosts. It is also possible that an 
endemic cycle exists involving arthropods other than the known 
primary mosquito vectors. In this case, these other arthropods 
may overwinter the virus, by either or both of the above 
mechanisms described for overwintering in the mosquito hosts. 

Clearly, there is an urgent need to establish the mechanisms 
responsible for successful overwintering of mosquito -borne viruses 
in Canada. We must be able to identify endemic foci, if present, 
and determine the contribution of both primary and alternate 
arthropod vectors. Without this knowledge, reasonable predictions 
on factors affecting disease outbreaks cannot be expected. 

California Group Viruses 

Four California group viruses are known from Canada: 
Snowshoe Hare virus, Jamestown Canyon virus, Trivittatus virus, 
and California Encephalitis virus. 

California Encephalitis (CE) has been isolated only from 
Manitoba in Canada (Artsob et al 1985) , and though known to cause 
disease in humans, is of little importance in this county at the 
present time. Transmission probably involves primarily Aedes 
spp., but CE virus has been isolated from other general (Turell 
and LeDuc 1983) . Transovarial transmission may be a possible 
overwintering mechanism among vectors of CE virus. Smart et al. 
(1972) and Crane et al. (1977) have provided evidence that CE 
virus was transovarially transmitted by Ae. dorsalis in Utah. 
However, Reeves (1977, in LeDuc 1979) has not been able to find CE 
virus in overwintering Ae. melanimon in California. More research 
is needed before any conclusion can be reached. 

Trivittatus virus is also present in Canada (Artsob 1983) 
and is of little importance at the present time. Aedes 
trivittatus is probably the primary mosquito host (LeDuc 1979) . 
Overwintering via transovarial transmission was first suggested by 
Pinger et al. (1975) and Watts et al. (1976), and later confirmed 
in the field by Andrews et al. (1977). 

Jamestown Canyon (JC) virus is apparently associated with 
white-tailed deer (LeDuc 1979), and not known to cause disease in 
man. Very little information is available on JC virus maintenance 
in the field, but Berry et al. (1977) did isolate the virus from 
larval Ae. triseriatus in Ohio. This is the only known record for 
overwintering of JC virus. Obviously, a great deal remains to be 
done to develop a meaningful understanding of overwintering for 
this virus. 

Snowshoe Hare virus is one member within the California 
group viruses for which there is good evidence that mosquito 
vectors are important sources for winter maintenance. This virus 
has repeatedly been isolated from larvae of various univoltine 
Aedes spp. in the North, including Ae. communis, Ae. hexodontus , 

38 



Ae. canadensis and Ae . implicatus (McLean et al. 1975, 1977; 
McLintock et al. 1976). Despite these isolations, however, 
definitive studies on subsequent transmission by adults of these 
various Aedes spp. have not yet been done. Further south, 
Culiseta inornata may be an important overwintering source for 
Snowshoe Hare virus. CuliseCa inornata has the ability to 
transmit the virus (McLean et al. 1974) and to survive and remain 
infected for extensive periods at low temperatures (McLean et al. 
1975). Again, however, Snowshoe Hare virus has not been isolated 
yet from overwintering, blood- fed adult Cs . inornata, and the 
exact role of Cs . inornata for maintaining the virus is not known 
(LeDuc 1979) . 

Although there is good evidence for transovarial 
transmission and overwintering for some California group viruses 
(e.g., LaCrosse and Keystone, see Watts and Eldridge 1975, Tesh 
1984), found in Canada, the evidence is still largely 
circumstantial. Hypotheses developed so far are based on infected 
larvae recovered from the field, early appearance of 
seroconversion in sentinel hosts, or transovarial transmission in 
the laboratory. We are still a long way from determining the 
importance of mosquito vectors in overwintering virus maintenance 
in terms of epidemiology of the various California group viruses 
found in Canada. 

St. Louis Encephalitis Virus 

There are no Canadian studies in which overwintering SLE 
virus in arthropod vectors has been investigated. Inference must 
be made from research conducted in the United States. 

All known primary mosquito vectors either survive the winter 
as hibernating adults (Culex pipiens pipiens , Cx. tarsalis) or as 
actively reproducing populations {Cx. pipiens quinquefaciatus, Cx. 
salinarius) . Only Cx. pipiens and Cx. tarsalis occur in Canada 
and may be involved in SLE virus transmission. Most overwintering 
females do not initiate host seeking and blood feeding prior to 
hibernation (e.g., Bellamy and Reeves 1963; Wilton and Smith 
1985) . SLE virus has been isolated from overwintering mosquitoes 
(Bailey et al. 1978), but their ability to transmit the virus in 
spring remains to be shown. Although a possible component to SLE 
epidemiology, overwintering of the virus in previously blood- fed 
hibernating female mosquitoes is perhaps of minor importance at 
best. 

The ability of other arthropods to transmit and overwinter 
SLE virus is poorly known. Although Aedes spp. transovarially 
transmit California group viruses (bunyaviruses) and have been 
reported as carrying SLE virus, they have not been implicated in 
overwintering SLE virus in the field. SLE virus has been isolated 
from mites (Dermanyssus spp., Ornithonyssis sp.) and ticks 
(Dermacentor variabilis , Argas arboreus) (see Mitchell et al. 
1980), but their role in the epidemiology of SLE is unknown. 

Although not yet demonstrated in field populations, 
transovarial transmission of SLE has been demonstrated 
experimentally under laboratory conditions. Two Aedes spp. 

39 



(epactius and albop ictus) , Cx. pipiens and Cx. tarsalis 
successfully transmitted virus to their offspring (Francy et al . 
1981, Hardy et al. 1981, Tesh 1984), the efficiency of which may 
be temperature related (Hardy et al . 1981). Hardy et al . (1981) 
and Nayar et al. (1986), have also provided additional support for 
vertical transmission of SLE virus in both Culex and Aedes spp. 

Western Equine Encephalitis 

There is no evidence to support transovarial transmission of 
Western Equine Encephalitis virus to provide the overwintering 
population of Culex tarsalis with a source of virus. In Canada, 
as in most of its range, adult nulliparous females overwinter in a 
condition of ovarian diapause (Bellamy and Reeves 1963; Spielman 
and Wong 1973). Thus, without evidence for transovarial 
transmission, it is unlikely that the principal vector for WEE 
virus can contribute to maintenance of the virus over winter in 
Canada. There is only one report of WEE isolation for 'over 
wintering' Cx. tarsalis . Blackmore and Winn (1956) collected WEE 
virus from a single pool of Cx. tarsalis during December in 
Colorado. However, it was not shown whether infected mosquitoes 
could survive until spring. 

Culex tarsalis can retain WEE virus and subsequently 
transmit the pathogen to a vertebrate host after at least 109 days 
at reduced temperatures (Bellamy et al. 1958). It is, therefore, 
possible that under climatically favourable conditions in part of 
its range, dormant Cx. tarsalis may maintain the virus. 

The role of alternate invertebrate vectors as a possible 
mechanism for overwintering WEE virus has been investigated, but 
as yet no positive results are available. Reeves et al . (1947) 
isolated WEE virus from the bird mite Liponyssus sylvarium in 
California, but the role as an overwintering source has not been 
substantiated. The swallow bug, Oeciacus vicar ius , though capable 
of overwintering a serologically similar virus, Fort Morgan, is 
incapable of transmitting WEE virus (Calisher et al. 1980). WEE 
virus has been isolated during the summer from numerous presumably 
secondary mosquito vectors, including Aedes, Anopheles , Culiseta, 
and Mansonia species. There has been insufficient research to 
conclusively eliminate these vectors as a possible means of 
overwintering WEE virus, though a high probability of success is 
unlikely from what we know at the present time. 

Eastern Equine Encephalitis (EEE) 

Although there have been numerous attempts to isolate EEE 
virus from overwintering vector mosquitoes or to demonstrate 
vertical transmission of the virus, there have been very few 
successes (Rosen 1987). Only once (Hayles et al. 1960) has EEE 
virus been isolated from Cs . melanura larvae in the field, as 
possible evidence for transovarial transmission. EEE virus has 
been isolated from mosquitoes (Chamberlain and Sudia 1961) , but as 
Rosen (1987) points out, this could have been the result of 
contamination from infected females. Watts et al. (1987) failed 
to detect transovarial transmission in either Cs. melanura, Ae. 

40 



cantator or Hansonia perturbans . Considering the overwhelming 
evidence against EEE virus overwintering in mosquito vectors in 
the United States, and considering that EEE virus has not yet been 
isolated from field-collected mosquitoes in Canada, it is probably 
safe to conclude that this mechanism for overwintering in a 
mosquito vector is of no consequence in the epidemiology of EEE in 
Canada at the present time . 

Summary 

The evidence for mosquito vectors serving as an 
overwintering mechanism for arboviruses was summarized by Rosen 
(1987) . For the California group viruses found in Canada 
(Snowshoe Hare, Jamestown Canyon, Trivittatus , and California), 
there is ample evidence to support transovarial transmission as a 
means for maintenance of the viruses, though other mechanisms may 
be involved as well. For St. Louis encephalitis virus (a 
Flavivirus) , the evidence is weak, and considerably more research 
is required before any conclusions can be made. For the two 
Alphaviruses found in Canada (WEE and EEE) , there is no evidence 
that mosquito vectors contribute to maintenance through the 
winter. 



41 



4. SURVEILLANCE 

a. Larval and Adult Surveys 
i . Larval Surveys 

Larval surveys are used to identify the sources of problem 
mosquitoes, and to determine their relative abundance. This 
information is essential to the operation of an efficient control 
program. 

Equipment 

A white enamel or plastic dipper, about 10 cm in diameter, 
is most often used for collecting mosquito larvae. Small larvae 
are most easily seen against the white background. Usually a long 
wooden handle is attached to allow easier sampling. 

A large squeeze bulb syringe of the type used for food 
basting is useful for sampling breeding sites unsuited for 
dipping, such as tree holes or rock crevices. For deep holes a 
length of tubing can be added to the syringe. A flashlight can 
also be used to improve visibility under these conditions. 

During extensive field sampling, a supply of small, screw- 
cap vials containing 70% alcohol should be on hand. Larvae can be 
transferred from dippers to these vials with eye-dropper pipettes. 
A note book should be carried to record field data. A strainer is 
useful to transfer larvae to clean water when sampling dark- 
colored or particle -laden water. Rubber wading boots are 
usually essential to sample an area thoroughly. 

Procedures 

In water bodies on the ground, mosquito larvae are usually 
found around the margins, associated with emergent vegetation and 
debris. When dipping is planned, the water body must be 
approached slowly and carefully. If the water is disturbed or a 
shadow cast, mosquito larvae often dive to the bottom and can not 
be collected in a dip sample. Because larvae tend to "bunch up" 
rather than being uniformly distributed, it is often necessary to 
sample several parts of a water body. Each site should be sampled 
frequently during the breeding season. 

Collected larvae can be preserved in alcohol -filled labelled 
vials soon after collection for later identification. If 
possible, larvae should be heat-killed by placing them in hot 
water. Some or all larvae can be kept alive and raised through to 
adults as an aid to identification. 

Accurate field notes are important. Each water body should 
be given a code designation and described, and a notation should 
be made of the date, number of dips made, number of positive dips, 
and an approximation of the number of larvae collected. The 
species found should be added upon identification. 

ii. Adult Surveys 

Adult mosquito surveys provide information on the relative 
abundance and seasonal and spatial distribution of species in an 
area. This can be important in providing forewarning of a disease 

42 



potential by producing data on known vector species. Adult 
surveys can also serve to evaluate on-going control programs. 

Light Traps 

Traps utilizing light as an attractant are widely used as a 
method of surveying adult mosquitoes. The most commonly used trap 
is the New Jersey trap, which has a standard household light bulb 
and requires a 110 volt source of electric power. An automatic 
timer or photo-cell can be used to control the trap so it operates 
only during hours of darkness. This is a durable, low maintenance 
trap that attracts large numbers of mosquitoes. 

The New Jersey traps' requirement for a 110 volt power 
source restricts its use. For remote areas or other situations 
where electricity is not available, a trap known as the CDC 
miniature light trap can be used. This is a battery powered trap 
with a small flashlight -type bulb as an attractant. Usually the 
batteries will provide only one night trapping and therefore the 
CDC trap, while portable, requires considerable maintenance. This 
trap usually catches fewer mosquitoes than the New Jersey trap. 

The CDC trap is often used to collect living specimens. New 
Jersey traps usually kill the entrapped mosquitoes, although the 
killing jar can be replaced with a mesh bag for live- trapping. 
Carbon dioxide from dry ice may be used in conjunction with light 
to enhance a trap's effectiveness. 

Proper location of light traps is important. Traps should 
be installed so that the light source is 165 to 180 cm above the 
ground. Traps should be at least 9 meters from buildings, out of 
the wind as much as possible, and away from competing light 
sources . 

A number of factors must be considered when interpreting 
light trap catch data. There are considerable differences among 
mosquito species in their response to light. Depending on the 
species in the sample area, it may be necessary to use other adult 
sampling methods in conjunction with light traps to get meaningful 
data on the relative abundance of mosquitoes. Fluctuations in 
traps catch numbers do not necessarily reflect changes in the 
number of mosquitoes in the area. Light trap catches generally 
decrease during full moon periods. Also, trap catches are 
affected by changes in flight activity which are governed in part 
by environmental factors such as temperature and wind. 

The degree of accuracy of light trap surveys increases with 
the number of traps used, which depends mainly on the number of 
traps and the manpower available . 

Biting Collections and Landing Counts 

Collecting and counting mosquitoes as they bite or land to 
bite is an effective way of determining the relative abundance of 
species that feed on man and are which therefore potential 
vectors. Biting collections are made by sucking mosquitoes into 
an aspirator tube as they begin to bite, usually on the bare legs 
from knees to ankles. They are then blown into a killing or 
holding tube for subsequent identification. If mosquito numbers 

43 



are very high, biting collections may become impractical and 
landing counts are conducted. A landing index (no. of mosquitoes 
landing per unit time) is made by counting, and collecting if 
desired, mosquitoes landing on a certain area of the collector, 
such as the front of the pants, over a measured period of time. 

For reliable spatial and temporal comparisons, biting 
collections and landing counts should be standardized as much as 
possible. Sampling should be done at approximately the same 
relative time from day to day, and similar conditions regarding 
vegetation and wind exposure should be selected. Because of 
differences in attractiveness among individuals, it is desirable 
that the same people be used throughout a survey. Similarly 
colored clothes should be worn by all participants from day to 
day. 

The flexibility of biting and landing counts makes this a 
very useful method of surveying adult mosquitoes. Counts can be 
made over a wide area with little preparation, and can be done 
during daylight hours or, with the aid of a flashlight, at night. 

Bait Traps 

Traps using live animals or carbon dioxide (dry ice) have 
been developed for mosquito surveys. Such traps attract only 
biting insects and can be used in areas without electric power. 
However, they require daily maintenance as they are usually baited 
at dusk and the insects and bait are removed at dawn. Live animals 
also deserve special care, and procedures must be in compliance 
with all current Animal Care guidelines. 

Bait traps may be small, using a chicken, guinea pig, or dry 
ice as an attractant, or large enough to be baited with livestock 
such as calves. All such traps are equipped with a one-way 
entrance such as an inwardly- directed funnel or V-shaped slot. 
Where larger animals are used, traps with portable sides for 
installation after a given exposure period may be helpful. 

Resting Stations 

Many species of mosquitoes, especially Culex and Anopheles , 
are inactive during the day and may be found resting in dark, 
cool, humid sheltered places. Careful counting of mosquitoes in 
these daytime shelters can give a comparative index of population 
densities. Sites that should be examined include barns, culverts, 
bridges, caves, and animal burrows. A portable light source is 
essential for many of these areas. An experienced observer often 
can visually determine the sex and species present, as well as 
make counts without collecting the mosquitoes. Usually some 
specimens are taken for laboratory identification. If live 
specimens are required, such as for virus isolation, an aspirator 
and holding container are necessary. It is important that counts 
and collections be made at the same time of day and in the same 
manner for accurate comparisons of results. 



iii. Population Dynamics, Activity 

44 



Information on natural mortality and reproductive potential 
in Cx. Carsalis and Cx. p. pipiens is generally lacking. Most of 
the published information on the population dynamics of these 
species is based on laboratory colonies. A thorough review of 
their bionomics can be found in Mitchell et al . (1980). 

At 20 to 21 C , the development time for the larvae of Cx. 
Carsalis is 8 to 14 days, with a mean of 11 to 12 days. Allowing 3 
to 4 days for pupal development, the time from egg to adult is 
approximately 15 days (Brennan and Harwood 1953; Hagstrum and 
Workman 1971) . 

The average development time for larvae of the Cx. pipiens 
complex at 26 to 27 C is 6 days (Petersen and Willis 1972; 
Shelton 1973). Allowing 3 days for pupal development, the time 
from egg to adult is about 9 days. 

Estimates of adult survival rates in natural populations of 
Cx. tarsalis have been made by Nelson et al . (1978) and Reisen et 
al. (1983). From mark- release -recapture studies, Nelson et 
al. (1978) estimated daily survival to be in the range of 64 to 
77%. Reisen et al. (1983) estimated daily survival rates of 
resting females during May to August to be 74 to 87%. 

A statistical model of the population dynamics of Cx. 
tarsalis , based on biological studies, has been developed to 
quantify population increases in this species (Moon 1976) . The 
parameters of the population dynamics were based on the 
Bakersfield, California area. The reproductive season in that 
region is about 9 months annually (Bellamy and Reeves 1963; Reisen 
et al. 1986a). In Washington state, the active reproductive 
period is around 6 months (Anderson and Harwood 1966) , while in 
Manitoba it is approximately 4 months (Brust 1982) . 

Moon (1976) based his expected population increases on two 
week intervals, beginning 20 March. Calculating 2+ gono trophic 
cycles by 17 April, an expected population increase from 1046 to 
39,537 was predicted over 4 months. This increase was based on an 
adult daily survival rate of 85%. 

An increase in trap catches of Cx. tarsalis of this 
magnitude occurs over a much shorter period of time in regions 
where this species has been studied. In Manitoba, a 10 to 30 fold 
increase in Cx. tarsalis females trapped occurred within a 2 to 3 
week period (Brust 1982) . However it is not known whether the 
size of trap collections reflect population levels or primarily 
flight activity levels. 

Raddatz (1985) developed a biometeorological model that 
related Winnipeg's mean daily count of Cx. tarsalis (total daily 
counts averaged over one week periods) to the antecedent (3 week 
lag) period of temperature and precipitation. The effect of the 
weather over the trapping period was partially accounted for by 
the multiplicative activity- level factor which was an exponential 
function of mean daily temperatures (mean daily maximum and 
minimum temperatures averaged over one week periods) . This factor 
had a value of 1.00 for a mean daily temperature of 15 C, dropping 
to 0.22 for C and rising to 2.72 at 25 C. In this way the model 
was able to predict trap collections of Cx. tarsalis, and 

45 



presumably population size, 3 weeks in advance of the collections. 

The number of generations of Cx. tarsalis in Manitoba is 
also affected by environmental conditions, mainly seasonal 
temperatures and the timing and amount of precipitation. 

Undoubtedly the timing of adult emergence from winter 
hibernation sites is important in the dynamics of this species. 
Over a period of 10 years (1975 to 1984) the dates of the first 
Cx. tarsalis male(s) trapped in Winnipeg in spring ranged from 11 
May to 26 June, with a median date of 6 June (Ellis 1984). The 
first Cx. tarsalis egg rafts collected over a 5 year period in 
Winnipeg, Manitoba (1980 to 1984) ranged between 7 May and 14 
June (Brust unpublished). During 1980 to 1984, egg rafts were 
found up to a month before females were captured in light traps in 
the Winnipeg region, possibly because the overwintering survival 
of females may be so low that they are rarely taken in light 
traps . 

The dates of the first light trap collection of Cx. tarsalis 
in Winnipeg, and the rapid increase in the counts each year 
(Raddatz 1985) would suggest that light traps usually capture 
females from the first summer generation. If the median date of 
the first light trap collection, 6 June, is considered to be the 
mean emergence date for the first generation and if females 
acquire a blood meal by one week post-emergence, then three 
generations of Cx. tarsalis are possible by the end of August 
(Buth 1983). 

In the western United States, overwintering females of Cx. 
tarsalis are nulliparous and do not seek blood meals (Bellamy and 
Reeves 1963; Mitchell 1981). There are several factors that 
indicate females of Cx. tarsalis emerging after mid- August in 
Manitoba do not seek a blood-meal and would therefore not be 
involved in vectoring WEE virus . The numbers of females that come 
to C0 2 traps (Brust unpublished) , sentinel chicken flock traps 
(Brust 1982) and light traps (Brust 1982; Raddatz 1985) decrease 
rapidly after mid-August. Egg rafts in ovipools are most numerous 
during late July and early August in Winnipeg, and may be 
collected until early September. The population arising from 
these should be sizable and trap collections should remain high 
when evening temperatures are above the threshold for flight. If 
these females do not seek hosts, the August decrease in Cx. 
tarsalis in sentinel chicken flock traps and the C0 2 traps in 
Manitoba is to be expected. The simultaneous decrease in the 
light trap collections suggests that diapausing females may also 
not be attracted to lights. 

An alternative hypothesis to explain the rapid August 
decrease in adult Cx. tarsalis counts in light, C0 2 , and flock 
traps is that there is a marked decrease in the population after 
mid-August. From a meteorological perspective, the annual mean 
daily temperature curve which normally peaks (21 C for Winnipeg) 
during July, drops to levels similar to mid- June (16 to 17 C) by 
late August. If Cx. tarsalis activity levels are exponentially 
related to mean daily temperatures (Raddatz 1985) , the seasonal 
drop-off of temperatures would have a significant effect on trap 

46 



counts and therefore on population levels. 

Autogeny is known to occur in field populations of Cx. 
tarsalis throughout the range of this species in North America. 
California populations may have autogeny rates as high as 90 to 
95% (Spadoni et al. 1974) and these rates decline during the fall 
(McDonald 1975; Moore 1963; Reisen et al. 1983; Spadoni et al. 
1974) . Further study is needed to determine if the decrease in 
autogeny in the fall is due to the same factors that produce 
gonotrophic inactivity in anautogenous females (Reisen 1986) . 

In Ontario, during 1978 to 1980, Cx. p. pipiens entered 
diapause in early July, with more than 90% of the field population 
in diapause by mid-August (Madder et al. 1983a). Some females 
continued laying eggs in the field until 15 October (Madder et 
al. 1980). There were three generations from May to September 
(Madder et al. 1983b). 

iv. Interpretation of Trap Data 

Various methods have been used to collect vector mosquitoes 
for virus isolation and to evaluate the effectiveness of vector 
control programs. An extensive review of mosquito sampling 
methods may be found in Service (1976) . 

The most commonly used trap for live collections of 
mosquitoes for surveillance of mosquito -borne pathogens in North 
America is the Centre for Disease Control (CDC) miniature light 
trap (Sudia and Chamberlain 1962), supplemented with dry ice 
(Newhouse et al. 1966). For the purpose of collecting infected 
vectors of WEE or SLE viruses the dry ice baited CDC trap collects 
a significant proportion of parous (potentially infected members 
of the population) females (Meyer et al. 1975). The efficiency of 
vector surveillance may be improved by combining a CDC trap with 
an oviposition site attractive to Culex spp.(Reiter 1983; 
Surgeoner and Helson 1978) . 

For the purpose of estimating population density, CDC dry 
ice baited traps capture larger numbers of female Cx. tarsalis 
than New Jersey light traps (Milby et al. 1978). 

Culex pipiens complex females are less readily attracted to 
dry ice. In Ontario, the New Jersey light trap captured as many 
Cx. p. pipiens and Cx. restuans females as the CDC dry ice baited 
trap (Copps et al. 1984). In the southern and eastern United 
States, Cx. pipiens quinquefasciatus is even less attracted to dry 
ice baited CDC traps than Cx. p. pipiens. Other collecting 
methods must be used such as cone or shed traps baited with 
chickens (Bowen and Francy 1980; Mitchell et al. 1980). Chicken- 
baited shed traps (Rainey et al. 1962) have been used effectively 
to collect Cx. tarsalis in southern Canada (Brust 1982; McLintock 
et al. 1966; Shemanchuk 1969). 

Standard New Jersey light traps are commonly used by 
mosquito control districts in North America to monitor seasonal 
mosquito activity. Their primary uses are to determine where 
adulticiding may be needed within the district, to evaluate the 
level of control achieved. 

The trap counts of vector species are used to assess the 

47 



daily activity of vectors during the season and to compare their 
activity over a number of years. Olson et al. (1979) analyzed 21 
years of light trap catches of Cx. tarsalis from 55 Mosquito 
Abatement Districts in California and were able to associate light 
trap indices (LTI - number of females per trap per night) of Cx. 
tarsalis with the activity of WEE and SLE viruses. 

The critical level of light trap counts of Cx. tarsalis in 
urban areas of California, below which no human cases of WEE or 
SLE were reported, was a LTI of 0.1. Peaks in the annual 
incidence of WEE or SLE occurred during those years when seasonal 
averages in urban areas reached a LTI of 21. Weekly incidence of 
human cases in urban areas was associated with a LTI of 21 for SLE 
and a LTI of 81 for WEE cases. In rural areas, human cases of SLE 
occurred when Cx. tarsalis averaged a LTI of 0.4 to 0.6 for the 
season. The average LTI for Cx. tarsalis must be > 0.1 before 
human cases of SLE or WEE would be expected in California. 
However, human cases may have been contracted when and where 
vector populations were much higher than the state average for the 
season. 

The critical level for Cx. tarsalis abundance, in regard to 
the epidemic spread of WEE to humans in California, was estimated 
to be a LTI > 10 (Reeves 1971) , or a C0 2 baited CDC trap index > 
30 (Reisen et al. 1984). Analyses of light trap data rarely 
consider the environmental conditions, if known, that prevent or 
hinder flight activity in mosquitoes. These factors must be 
considered when interpreting trap counts as an index of virus 
transmission. 

There is a threshold temperature, depending upon the species 
and the latitude, below which little or no flight to traps occurs 
regardless of the size of the resident mosquito population. In 
Winnipeg, Manitoba, the number of Cx. tarsalis collected in New 
Jersey light traps increases as the temperature increases above 15 
C, and decreases below that temperature (Raddatz 1985). The 
threshold temperature for flight in Cx. tarsalis , on the basis of 
light trap collections, is about 8 to 10 C (Brust and Ellis 
1976a). On a seasonal basis, the assumption is frequently made 
that an equal number of warm and cool nights will occur each year 
and that the years can therefore be compared. However this is 
unlikely to occur. Analyses of light trap counts in the future 
should use available temperature data from the immediate area 
(e.g. Raddatz 1985). Any conclusions drawn made about population 
levels from trap counts which have not been adjusted for weather 
changes must be suspect. 

Other environmental factors that may affect the numbers of 
mosquitoes collected in traps , include relative humidity or vapour 
pressure deficits (Clark et al. 1976), mean nightly wind speeds, 
moonlight, physiological state of the females (Bidlingmayer 1985), 
and both the specific and the general trap location (Copps et al . 
1984). 

The physiological state of the female mosquito (such as 
nulliparous, gravid, or parous) influences the collection of 
vector mosquitoes in different kinds of traps. Meyer et al. 

48 



(1975) found that C0 2 -baited CDC traps collected more parous 
females of Cx. Carsalis than did New Jersey light traps. However, 
Magnarelli (1975) found the reverse in Cx. restuans, and 
Feldlaufer and Crans (1979) found that New Jersey light traps 
collected more parous Cx. salinarius then did the same trap baited 
with dry ice. Resting box collections may be less biased towards 
any particular physiological state and the greater percentage of 
nulliparous mosquitoes usually found in resting boxes (Meyer eC 
al. 1975; Nelson 1964) may reflect the natural population more 
accurately. 

b. Virus Activity 

i. Mosquito Populations 

Recovery of WEE and SLE virus from Culex vectors is an 
important surveillance tool, because it determines the potential 
for virus transmission to humans. However, human case incidence of 
WEE and SLE viral infections is not always correlated with virus 
infection rates in vectors because the findings do not 
differentiate between infected individuals and infective ones 
(Bowen and Francy 1980) . The significance of infection versus 
transmission rates in vectors has been reviewed by Reeves et 
al.(1961) and the factors influencing vector competence have been 
reviewed by Hardy et al. (1983), McLintock (1978) and Mitchell 
(1983a). 

Surveillance for virus activity in mosquitoes was begun in 
Canada in 1942, when the Manitoba Department of Health and 
Welfare, in conjunction with the Children's Hospital of Winnipeg, 
began a study of the relationship between mosquitoes and WEE virus 
in Manitoba (McLintock 1946, 1947, 1948). Subsequently, 
surveillance for virus activity in mosquitoes has been carried out 
for other viruses causing human illness (McLean 1975, 1979; 
Mclintock and Iversen 1975; Artsob and Spence 1979). 

The 1975 outbreak of WEE in Manitoba resulted in a decade of 
surveillance of WEE virus activity in that Province. Subsequent 
outbreaks were studied in more detail than the one in 1975 but not 
all of these have been published. Results on the 1975 outbreak 
can be found in Sekla (1976) and on the 1977 and 1981 WEE 
outbreaks in Sekla (1982). Virus activity, other than WEE, was 
also monitored in mosquitoes from Manitoba (Sekla et al . 1980; 
Sekla and Stackiw 1982) . Results of the environmental studies 
conducted during the 1983 WEE outbreak in Manitoba are in a report 
by Manitoba Environment, Workplace Safety and Health (1984). 

During two WEE epidemic years in Manitoba, the number of WEE 
virus isolations from mosquitoes ranged from 71 isolations in 1977 
to 32 in 1981. Of these 33 and 18 respectively were isolated from 
Cx. Carsalis. During 4 non-epidemic years, the number of WEE 
virus isolations ranged from to 4. None of these were from Cx. 
Carsalis (Sekla and Stackiw 1982). In 1977, the seasonal 
infection rate in Cx. Carsalis was 1:347. In 1981 it was 1:283. 
In North Dakota, during the epidemic year 1975, the seasonal 
infection rate was 1:500 Cx. Carsalis (Monath 1979). 

In Saskatchewan, the infection rates of WEE virus in Cx. 

49 



Carsalis were a seasonal average of 1:145 Cx. Carsalis in 1963 and 
1:169 in 1965. Both years were outbreak years (McLintock eC al . 
1966; McLintock eC al . 1970). As in Manitoba during 1976 to 1981, 
WEE virus was not isolated from Cx. Carsalis during non-epidemic 
years . 

In Alberta, WEE virus was isolated from Cx. Carsalis 
collected from mammalian burrows during 1965. The infection rate, 
calculated on the number (1141) of females of this species 
examined for blood, was 1:285 Cx. Carsalis . No human cases were 
reported that year in Alberta but there was an epizootic amongst 
equines and there were human cases in Saskatchewan (Artsob and 
Spence 1979; Morgante eC al. 1968; Shemanchuk and Morgante 1968). 

Infection rates of WEE and SLE viruses in Cx. Carsalis may 
change during the season. When this occurs, the rate increase 
must be monitored carefully to evaluate potential risk to humans 
(Reeves and Hammon 1962). In Saskatchewan, McLintock et al. (1970) 
found that the WEE virus infection rate in Cx. Carsalis reached a 
weekly high of 1:43 whereas the seasonal average was 1:145 during 
the epidemic year of 1963. During the 1965 epidemic year in 
Colorado, WEE virus infection rates in Cx. Carsalis increased from 
1:667 (1.5/1000) on 13 June to 1:67 (15/1000) by 18 July. By 25 
July, the infection rate began to decrease (Hess and Hayes 1967). 

The method of vector collection may affect the rate of virus 
recovery. More efficient methods of collection of potentially 
infected females need to be considered when surveillance is 
undertaken. A trap that combines an oviposition pool attractive 
to the vector species, which selectively captures gravid females, 
increases the chances of isolating a mosquito -borne pathogen 
(Surgeoner and Helson 1978) . By reducing the size of the 
oviposition container, thereby forcing gravid females to fly 
closer to the suction fan, Reiter (1983) was able to capture most 
gravid females before they oviposited and escaped. In Memphis, 
Tennessee, he obtained 141 Culex females per oviposition trap 
night versus one female per resting box collection and 0.4 females 
per New Jersey light trap night. 

ii. Sentinel Flocks 

The use of domestic chickens to monitor WEE and SLE virus 
activity has been widely adopted in North America (McLintock eC 
al. 1966; Rainy et al. 1962; Reeves and Hammon 1962; Wong et 
al. 1976). 

Chickens infected with WEE virus become viremic within 1 or 
2 days , remain infective for 2 or 3 days and then become immune 
(Bellamy et al. 1967; Wong et al. 1976). Sentinel chickens are 
usually bled every two weeks, allowing sufficient time for 
antibodies to develop to detectable levels (Wong et al. 1976). To 
be an effective early warning of an impending epidemic, chickens 
should be placed on location as soon as vectors appear in the 
spring. Sentinel chickens that develop antibodies should be 
replaced immediately with new birds to maintain the flock size, 
exposure rate and attraction to mosquitoes remains at a constant 
level (Bowen and Francy 1980) . 

50 



Wild birds 

Wild birds are frequently surveyed to establish antibody 
prevalence to WEE and SLE viruses (Bowen and Francy 1980; Burton 
et al. 1966; Burton and McLintock 1970; Dorland et al . 1979; Hayes 
et al. 1967; Hess and Hayes 1967; Holden et al . 1973; Reeves and 
Hammon 1962) . If only juvenile birds are sampled or if juveniles 
are carefully separated and the results are tabulated separately 
from those from the adults, the data will more accurately reflect 
viral activity for the year. Sparrows are most frequently 
collected using mist nets. Repeated samples, weekly or biweekly, 
of 100 to 150 birds from several sites are necessary to provide an 
adequate early warning of viral activity in a geographic area 
(Bowen and Francy 1980) . Meaningful assessment of antibody levels 
depends upon the availability of background data from previous 
epidemic and non-epidemic years, and upon serial measurements from 
spring to fall. A sudden or gradual increase in antibody level in 
juvenile birds may be highly significant (Bowen and Francy 1980) . 

iii. Reservoirs, Indicators 

Vertebrate reservoirs may play three important functions in 
epidemiology of mosquito -borne viruses. They may serve to amplify 
virus levels in spring as capable vector species first become 
active. They may serve as maintenance hosts for the virus 
throughout the summer and a pool of virus available for vectors to 
spread the virus to other epizootic or epidemic hosts. Finally, 
as rates of transmission decrease in autumn with reduced vector 
activity, the vertebrates may be overwintering reservoirs for the 
virus . 

If wild vertebrates, either birds or mammals or both, are 
critical to initiation of virus introduction, maintenance and 
spread, then intuitively, they might be used effectively in a 
surveillance program as an early warning system for possible 
disease outbreaks. Limited serosurvey work for mosquito -borne 
virus activity has been done in Canada. Meaningful surveillance 
of wild vertebrates must rely on a clear understanding of the 
specific vertebrates involved, and their roles as they affect 
distribution and abundance of the virus. Information must be 
available on reproductive patterns, exposure and availability to 
vector mosquitoes, response to virus infection, serological 
response following active infection, and patterns of movement 
(dispersal and migration) . Trained personnel are required in the 
field to collect the appropriate verebrate species and to take 
blood samples. Extensive data are necessary for several out break 
and nonoutbreak years before critical levels of virus activity in 
vertebate populations can be associated with pending outbreaks. 

Only one mosquito -borne virus warrants consideration of wild 
vertebrate surveillance in Canada, viz Western Equine Encephalitis 
Virus. Eastern Equine Encephalitis Virus and the known 
Californian Group Viruses are not prevalent enough to justify 
extensive surveillance. There has been only one epidemic of St. 
Louis Encephalitis, in Ontario in 1975, and although antibodies 

51 



have been detected in both resident English sparrows, and 
migratory passerines (see Artob and Spence 1979), extensive effort 
to monitor wild birds seems unjustified at the present time. 

The history of Western Equine Encephalitis Virus is marked 
by epizootic outbreak years in the Prairie Provinces. Wild 
vertebrates have been examined for evidence of virus infection and 
many species have been implicated. Antibodies have been detected 
in ducks, blackbirds, pigeons, English sparrows, barn swallows, 
starlings, ruffed and sharp- tailed grouse, Swainson's hawks, 
gulls, magpies and robins (Burton et al. 1961; Burton et al . 
1966b). Seropositive mammals include Richardson's and Franklin's 
ground squirrels, snowshoe hares, red foxes, skunks, reindeer, 
bison, moose, pronghorn antelope, red-backed voles, weasels, and 
muskrats (Burton et al. 1966b; Gwatkin and Moynihan 1942, Leung et 
al. 1975; Yuill and Hanson 1964; Burton and McLintock 1970; 
Trainer and Hoff 1971; Barrett and Chalmers 1975; Hoff et al. 
1970; Sekla and Stackiw 1982). Virus and neutralizing antibodies 
have also been isolated from garter snakes and leopard frogs 
(Burton et al. 1966a; Spalatin et al. 1964; Prior and Agnew 1971). 
These numerous isolations were, however, detected in trying to 
establish the existence and/or role of wild vertebrates in the 
western equine encephalitis cycle. Until these factors are known, 
surveillance activity for wild vertebrates in Canada will be 
inefficient or of little value. 

Western Equine Encephalitis Virus outbreaks have been 
unpredictable in time and space. Even by concentrating on species 
of vertebrates in which levels of virus activity may be an 
indication of later season activity (e.g. English sparrow - Hess 
and Holden 1958) , the amount of effort and expenditure of 
resources may not be justified on the basis of the return. More 
valuable information would be generated by placement of sentinel 
vertebrates (e.g. chickens or equines) in strategic locations. 
Sentinel animals are more easily accessed, require fewer blood 
samples to be processed, and have a known history of virus 
exposure and antibody response . 

In conclusion, it is apparent that it is not feasible to 
introduce wild vertebrates into arbovirus surveillance programs in 
Canada at the present time. Unless we gain additional information 
on the role of wild vertebrates in the virus cycle, and unless 
there is evidence that certain species provide better correlation 
of virus activity and disease outbreaks than existing techniques, 
implementation of vertebrates as a surveillance tool is 
unwarranted. 

c. Criteria 

1. Mosquito Counts 

When WEE or SLE viruses are detected in vector mosquitoes , 
the size of the vector population is an important factor in the 
spread of these viruses to humans (Brust 1982; McLintock et al. 
1966; Reeves 1965; Reeves and Hammon 1962). The most common 
method of determining the relative size of the mosquito population 
and the mosquito species in an urban area, is the use of the New 

52 



Jersey light trap. Live trapping of mosquito vectors for the 
purpose of virus isolation may be accomplished by using a modified 
New Jersey type light trap (Brust 1982; McLintock 1946) but 
usually the CDC light trap baited with dry ice is used. The 
counts from each of these trap types may used to assess the 
relative population size during the season or from year to year. 
For Cx. tarsalis counts in California, a dry ice -baited CDC trap 
index of 30 females per trap night, compares to a New Jersey light 
trap index of about 10 per trap night (Milby et al. 1978; Reisen 
et al. 1984). 

New Jersey light trap collections have been used to estimate 
minimum levels of abundance of Cx. tarsalis females associated 
with WEE and SLE viruses in humans in California over the period 
1953 to 1973 (Olson et al. 1979). The LTI was calculated for both 
rural and urban areas. Because most abatement districts operate 
New Jersey light traps in urban areas, with a few rural sites, the 
LTI's from urban areas in California may be of greater value in 
assessing vector threshold levels of this species in the future. 
On a seasonal basis in California, the critical level of Cx. 
tarsalis counts, below which no human cases of these viruses were 
detected, was a LTI of 0.1. However critical levels of females 
associated with a significant number of human cases were between a 
LTI of 6.4 and 62.4. Peaks in the weekly incidence of SLE cases 
were associated with a LTI of 21 and of WEE cases with a LTI of 81 
(Olson et al. 1979). A LTI for Cx. tarsalis of > 10 is considered 
to be the critical level for WEE virus transmission to humans in 
California (Reeves 1971; Reisen et al. 1984). 

Mosquito counts from sentinel chicken shed traps , each 
containing 10 birds, have been used to calculate population levels 
of Cx. tarsalis associated with epidemic years in Manitoba (Brust 
1982). Both the numbers and the X Cx. tarsalis in the weekly 
collections were correlated with epidemic years. During epidemic 
years, > 20 females per trap week were collected during the last 
half of June and the first half of July. The threshold level for 
% Cx. tarsalis in the collections during this period was 25%. The 
number of and the % Cx. tarsalis in sentinel chicken shed trap 
collections were considerably below those levels during non- 
epidemic years (Brust 1982) . 

Seasonal light trap counts of Cx. tarsalis in Saskatchewan, 
using a modified New Jersey live trap, were higher during the 
epidemic year of 1963 than during the non-epidemic year of 1964 
(McLintock et al. 1966). McLintock previously used this trap in 
Manitoba during 1942 to 1948 and found that the Cx. tarsalis 
counts were highest during the epidemic year of 1947 (McLintock 
and Rempel 1963) . 

An analysis of 7 years of Cx. tarsalis counts (1977 to 1983) 
in New Jersey light trap collections from Winnipeg, Manitoba, was 
conducted by Raddatz (1985). Also a forecast count and an actual 
count was made for 1984. Two epidemic years had higher levels of 
Cx. tarsalis than 4 non-epidemic years. However, 1 epidemic year 
(1981) had lower counts than 2 of the non-epidemic years (1978, 
1984) (Raddatz 1985) , demonstrating that there may be exceptions 

53 



to the association of WEE human cases with abundance of Cx. 

carsalis . 

ii. Significance of Seroconversion 

Seroconversion in sentinel chickens is usually correlated 
with the appearance of human cases of SLE and human and equine 
cases of WEE (Bowen and Francy 1980; McLintock et al. 1970). In 
Manitoba, the increase in seroconversion in sentinel chickens 
occurred simultaneously with the increase in equine cases in 1975 
(Lillie et al. 1976; Wong et al . 1976). Human cases followed the 
equine cases by about 2 weeks (Waters 1976). However, human cases 
may not follow low, background levels of seroconversion. 

The level of seroconversion in sentinel chickens in Manitoba 
reached 50% during 1975 and 84% during 1981 (Wong et al. 1976; 
Wong and Neufeld 1982) . Seroconversion rates >20% per exposure 
period indicates high viral activity and, according to Wong and 
Neufeld (1982), can lead to an epizootic and an epidemic of WEE. 

In Saskatchewan, WEE virus seroconversion rates in sentinel 
chickens averaged 42% in 1963 and peaked at 92% by the end of 
August (McLintock et al. 1966). In Kern County, California, the 
highest seroconversion rate (50%) to WEE virus in chickens over a 
10 year period (1943 to 1952) was associated with the epidemic 
year of 1952. The seroconversion rate exceeded 20% (26 to 34%) in 
rural areas , where rates were higher than in urban areas , for 4 
other years ; the number of human cases of WEE during those years 
was greater than average in 1943 and 1945 but lower than average 
in 1949 and 1950 (Reeves and Hammon 1962) . 

During SLE epidemics in the United States, seasonal 
seroconversion rates in chickens have varied between 30 and 90% 
(Bowen and Francy 1980). However, one human case of SLE occurred 
in Kern County, California, when the seasonal seroconversion rate 
in chickens averaged only 2% (Reeves and Hammon 1962) . 

iii. Weather Factors 

Summer temperatures and precipitation may influence the size 
of vector populations such Cx. tarsalis (Fraser and Brust 1976; 
Raddatz 1985; Reeves and Hammon 1962). Wet spring conditions, 
followed by warm temperatures, have been associated with unusually 
rapid increases in Cx. tarsalis populations in Manitoba and 
California. 

Summer temperatures may affect the extrinsic incubation 
period of arboviruses, the transmission to vertebrate hosts and 
the extent of their geographic distribution (Hess et al. 1963). 
In California, WEE virus was detected in mosquitoes after 
temperatures exceeded 26 C for 2 weeks (Reeves and Hammon 1962) . 
When warm temperatures occurred earlier in the summer, during 
years when WEE virus was present, virus activity occurred earlier 
in California. When cool spring temperatures prevailed, virus 
activity was retarded. 

In Saskatchewan and Manitoba, the temperatures suitable for 
extrinsic incubation of WEE virus may be lower than those in more 
southern regions . Temperatures rarely exceeded 26 C in 

54 



Saskatchewan in 1963 or in Manitoba during 1975. Weekly means 
never reached 26 C in Manitoba during either 1975 or 1981 (Fraser 
1982; Fraser and Brust 1976; McLintock et al . 1966). The 
threshold temperature for extrinsic incubation of WEE virus in Cx. 
tarsalis is probably about 19 to 21 C (Mclintock et al . 1966). 
This would agree with the association of WEE epidemics with the 
geographic region above the 21 C June isotherm in North America 
(Hess et al. 1963). 

SLE epidemics are associated with geographic regions of 
North America that have a mean temperature of at least 21 C during 
June (Hess et al. 1963; Monath 1980). Only 1 SLE epidemic 
occurred in Canada, and this was limited to southern Ontario, a 
few hundred km north of the 21 C June isotherm. Temperatures 
during 1975 were above normal during May, June and July, and may 
have played a role in the northern spread of SLE that year 
(Bristow 1979). In California, SLE isolations have occurred later 
in summer than those of WEE and have followed periods when 
temperatures exceeded 28 C (Reeves and Hammon 1962) . 

Temperature affects the development and abundance of vector 
populations that transmit WEE and SLE viruses . This in turn 
affects the spread of these viruses to vertebrates during the 
spring amplification cycle and the spread to humans and other 
hosts during the summer months (Hess and Hayes 1967 ; McLintock et 
al. 1966; Reeves 1965). In Manitoba, a weekly mean temperature of 
16 C is significant in the development of Cx. tarsalis . Below 
this temperature, development is retarded or halted (McLintock 
1948) . According to McLintock (1948) , two other factors are 
important for Cx. tarsalis to become abundant in Manitoba 1) the 
average mean weekly temperature during the latter half of June 
must be above normal, and 2) the average mean weekly temperatures 
for July and August must be 2 C above normal. However, during 
1975 and 1981 in Manitoba these conditions were not met (Fraser 
and Brust 1976; Fraser 1982). New criteria are needed to 
determine which weather factors are important in the increase of 
Cx. tarsalis populations and the transmission of WEE virus to 
vertebrates . 

Daily mean temperatures below 15 C have been shown to be 
important in reducing trap collections, and therefore flight in 
Cx. tarsalis in Winnipeg, Manitoba (Raddatz 1985) . Based on 7 
years of light trap collections, Raddatz (1985) was able to model 
the effect that temperature, precipitation, evapotranspiration and 
runoff had on collections, and presumably on population size, of 
Cx. tarsalis in Winnipeg. The effect other weather factors have 
on trap collections (e.g. wind, relative humidity, and vapour 
pressure deficit) are reviewed by Bidlingmayer (1985). 



d. Provincial Surveillance 

i. Western Equine Encephalitis 

Epidemics of arboviruses occur when vector abundance and 
transmission of virus exceed thresholds at which the virus is 
carried over into human and equine hosts. Arbovirus surveillance 



55 



programs entail monitoring of adult populations of vector species, 
and virus transmission rate, virus isolations, and diagnosis of 
infections in natural and dead-end (including human) hosts. 

Provincial surveillance programs in Canada were reviewed in 
1980 - 1981 as part of the feasibility study for the Canada Biting 
Fly Centre (Appendix IV). At that time, annual surveillance 
programs for Western Equine Encephalitis were carried out in 
Manitoba and Saskatchewan. Since then, the Manitoban program has 
been terminated and the Saskatchewan program reduced. No annual 
programs are carried out in Alberta, British Columbia, the 
Maritimes, nor the Territories. Incidence of encephalitis 
infection in humans in recent years in these regions was nil. 

No other annual surveillance programs, except that in 
Ontario for SLE, are carried out in Canada. Human incidence of EEE 
infections have occurred in Quebec, but at levels too low to 
justify the expense of annual surveillance. The National 
Arbovirus Reference Centre in Toronto monitors incidence of human 
infections. 

Surveillance is carried out in the United States for several 
arboviral diseases, including WEE, EEE, and SLE, in the states 
bordering Canada 1 . These jurisdictions provide further input into 
Canadian surveillance programs, as well as an alert for the 
implementation of ad hoc surveillance by Canadian authorities. 

Manitoba 

Manitoba began surveillance in 1976, after the outbreak of 
WEE in 1975. The program was carried out by Manitoba Health, and 
co-ordinated, initially, by the Manitoba Arbovirus Surveillance 
Committee (1975-1983) and subsequently by the Western Equine 
Encephalitis Surveillance Committee (1984-1985). Both committees 
were made up of multi -agency, multi- disciplinary members who were 
scientists or other health professionals. The program was carried 
out to predict outbreaks of WEE in the human population and to 
recommend remedial action. Following an outbreak and extensive 
emergency mosquito control program in 1983, the fourth in seven 
years , the Manitoba Government reviewed both the efficacy and 
environmental monitoring of its emergency aerial spray program, 
and, separately, mosquito control in the province. The outcome 
of the review was a re -assessment of provincial procedures and 
requirements for WEE surveillance and control. The Province 
maintained its commitment to surveillance and assessment of risk 
of outbreaks , but rated emergency aerial spray measures as a 
strategy to protect the public as low priority. Control measures, 
if warranted, were to be focused on public advisories and personal 
protection. In 1986, the Government withdrew financial support 
for the program and surveillance was discontinued in April, 1986. 



^hio Vector Borne Disease Unit, Ohio State Department of 
Health; Mosquito Research and Control Group, Minnestota State 
Department of Health; Division of Environmental Sanitation, North 
Dakota State Department of Health. 

56 



The Province of Manitoba developed the most intensive 
arbovirus surveillance program in Canada. It consisted of 
monitoring of weather, abundance of mosquito populations 
(including Ae . vexans , Cs . inornata, Cx. restuans , as well as the 
primary vector, Cx. tarsalis) , virus activity as indicated by 
isolations from mosquitoes, infections in sentinel flocks, and 
horse and human infections (See CRITERIA 5a). The program also 
included exchange of monitoring data or assessments with 
neighbouring jurisdictions. The Manitoba Arbovirus Surveillance 
Committee (MASC) was comprised of specialists in medical 
entomology, epidemiology, veterinary medicine, virology, 
environmental management, insect control, meteorology, and public 
health. The mandate of the Committee was to determine risk of 
outbreak of disease, and to inform the Manitoba Minister of 
Health. 

The provincial program generated criteria for assessing risk 
on a province wide basis. Surveillance in Saskatchewan has been 
carried out for longer, but at a smaller, localized scale. 
Comparisons of programs are difficult because of differences in 
level of surveillance, approach to surveillance, and approach to 
protection of public health. Criteria developed in Manitoba were 
used to assess risk to public health and were also used in 
decision making on emergency aerial spraying of municipalities. 

Saskatchewan 

The WEE surveillance program is part of an annual arboviral 
surveillance program begun over 30 years ago. The program was a 
joint venture between the University of Saskatchewan (Department 
of Veterinary Microbiology) and the Agriculture Canada Research 
Station; now it is carried out by the University. The program 
consists of monitoring mosquito populations and virus activity(see 
CRITERIA 5a) . Mosquito populations are monitored using New Jersey 
style light traps in three selected sites, and virus activity is 
assessed by monitoring seroconversion rates sentinel chicken 
flocks and incidence of horse cases. The extensive database 
gained over three decades of monitoring and research enables 
experienced scientists to predict likelihood of outbreaks in some 
local areas . 

Ontario 

The province does not carry out routine surveillance for 
WEE, but keeps in regular contact with neighbouring jurisdictions 
for prediction of potential outbreaks. Incidence of WEE in 
Ontario is low; it was first recognized in the western region by 
horse infections in 1981, concurrent with an outbreak in 
Manitoba. WEE is not known to occur in provinces east of 
Ontario. 

Other Jurisdictions 

Local mosquito abatement authorities in Canada are too small 
and too scarce to provide a major component of surveillance and 



57 



control in province -wide surveillance programs. Some local 
authorities, e.g., in Manitoba the City of Winnipeg and the City 
of Brandon have the expertise and, in Winnipeg, the resources to 
make significant contributions, but this level of support is not 
typical. 

Following cancellation of the provincial program in Manitoba 
in 1986, the Insect Control Branch of the City of Winnipeg, 
concerned for its mandate to protect Winnipeg residents 
(representing over 50% of the provincial population) from WEE, 
implemented its own surveillance program. The program consists of 
monitoring virus activity both in mosquito populations and 
sentinel flocks on a reduced scale to that of former provincial 
program. The City routinely monitors mosquito populations with a 
system of 25 New Jersey style light traps within the City's 
control zone and additional traps outside the control zone. Five 
sentinel flocks traps of the design used by the province ( Wong et 
al . 1976, Wong and Neufeld 1982) are used in selected sites 
located across the City. Mosquito pools and sentinel flock blood 
samples, collected biweekly, are analyzed by the provincial public 
health laboratory. 

The City of Regina mosquito control program has two stated 
main objectives: to prevent major mosquito infestations from 
developing in breeding sites, and to monitor populations and 
identify various mosquito species present throughout the season, 
in particular those vectors of Western equine encephalitis (Ann. 
Rpt. Mosq. Control, City of Regina, 1988) 

In Alberta and British Columbia, population abundances of 
Cx. tarsalis axe monitored through local control operations. 
Municipal mosquito control programs in both these provinces are 
regulated by provincial authorities. Emergency monitoring of 
mosquito populations and virus activity are carried out when 
concern of outbreaks is raised as a result of high populations of 
vector species and identification of viral infections either in 
the provinces or in adjacent jurisdictions. 

Problems in Surveillance Programs 

Problems identified in Manitoba in carrying out surveillance 
and assessing risk of human infection stem in part from the 
decision-making process and from the options for remedial action, 
once the risk of outbreak was identified; and partly from 
shortcomings in surveillance procedures. Because of the low 
number of expert local control organizations and the inadequacies 
of larviciding for emergency measures, the Province resorted to 
emergency control measures 2 during each of the last four 



2 Control approaches followed in California, where 
surveillance and control programs have been carried out for 30 
years (Walsh 1987) and which represent the best available 
technology, are not applicable to Canada because of less severe 
health consequences and lower socioeconomic impacts of mosquitoes 
in Canada. 

58 



outbreaks. This history of reliance on emergency aerial spraying 
influenced decision making by the Committee. 

The decision-making authority to implement emergency control 
measures rests with the Minister(s) of Health. As a result of the 
Committee's role in developing the surveillance program, 
developing criteria to asses risk, and carrying out the program 
and assessing risk, the Manitoba Arbovirus Surveillance Committee 
was a major influence on decisions to implement emergency aerial 
spraying. The decision-making process lacked adequate separation 
of stages between identification of risk of human infection and 
the decision to implement emergency aerial spraying. 

Furthermore, effectiveness of remedial action is doubted: 
the 1981 emergency aerial spray was estimated by provincial 
officials to provide only 10% protection at best for the public 
(unpubl. Inter-Departmental Review Review Committee, Manitoba 
Government 1984) . Failure to achieve greater protection was 
considered primarily due to lack of exposure of Cx. tarsalis 
populations to adulticide because ULV aerial spraying does not 
penetrate well into resting sites and because federal regulations 
prohibit aerial application of insecticides during nightfall, 
i.e., during peak Cx. tarsalis activity periods. The 
effectiveness of emergency aerial spray in reducing incidence of 
WEE cannot be determined with precision; it can only be inferred 
based on differences in mosquito counts. 

The severity of WEE as threat to public health is also 
doubted. The lack of large numbers of either horse or human cases 
in outbreaks in Manitoba since the 1960's is indicative of a 
change in pattern of the disease. One possible explanation is a 
loss of virulence of the WEE virus occurring in the Canadian 
prairies. A second is the change in land use, for example, with 
increased urbanization in the southern regions of Canada, improved 
agricultural irrigation, and flood control systems, all of which 
have contributed to reductions in the extent of breeding sites. 
Considered in conjunction with changes in lifestyles (Gahlinger, 
Reeves and Milby 1986) , these changes have led to reductions of 
human exposure to the virus . 

Jurisdictions differ in attitude and approach to WEE as a 
threat to public health. The conditions considered necessary for 
outbreak of WEE in Manitoba have also been present concurrently in 
Alberta, and British Columbia, yet these provinces did not 
implement emergency aerial spray measures . No outbreaks occurred 
there, even though no large scale aerial spraying was carried out. 
Public and government attitude to WEE in these two provinces 
differ than that in Manitoba. 

Problems in assessing risk were also a result of variables 
ensconced in the surveillance procedures: 

Mosquito Trapping 

The variety of trapping techniques used to assess population 
abundances necessitated different interpretations of trap counts 
and differential emphasis on trap catches. For example, the 
program made use of NJLT data generated by three different 

59 



jurisdictions (the Province, the City of Winnipeg, and the City of 
Brandon) each employing its own modification of NJLT style trap. 
Difficulties in trap catch interpretations were also compounded by 
differences in trapping schedules, and trap strategy. The 
surveillance program used one set of mosquito traps to monitor 
both mosquito populations as well as to capture large enough 
samples of mosquitoes for viral analysis. Flock traps, light 
traps, and C0 2 -baited traps capture mosquitoes differentially, 
according to mosquito species, age, behavioural activity, as well 
as ambient (i.e. temperature, humidity and light intensity) 
conditions. 

Equine Cases 

Lack of data on frequency and extent of horse vaccinations, 
and lack of information on horse cases compromise the value of a 
relatively reliable indicator of impending human infections. By 
the time horse cases are identified, it may be too late to mount 
an effective emergency spray program, particularly one which is 
monitored for environmental impacts. It is also too late to take 
any action other than emergency spraying and public advisories on 
self -protect ion. 

Failure to Apply all Criteria in Assessing Risk 

Prior to 1981, the criteria on which the Committee based its 
decisions were poorly defined, in part because of an inadequate 
data base. After the 1981 emergency, the Committee developed 
more formal criteria using four indicators (see CRITERIA 5a) . 
However, these criteria were not followed consistently in 1983. 
That year, an initial assessment of high risk was based only on an 
unexpected early seroconversion of sentinel flocks. High mosquito 
numbers, virus in mosquitoes, and horses cases appeared later. 

The practice of hiring university students as seasonal 
assistants has led to gaps in the database for significant 
periods, e.g., April and late August and September. Surveillance 
is not carried out at times when data are still needed to assess 
threat of infection in late season, and to clarify virus cycle in 
late summer, early fall. 

ii. St. Louis Encephalitis 

Ontario is the only province in which significant SLE 
activity and human cases have been recorded. Following the only 
reported outbreak in 1975, a document was prepared by the 
Committee on Programs for the prevention of Mosquito -borne 
Encephalitis, for the Ontario Ministry of Health (Mahdy et al. 
1979). In that report, provincial surveillance activities were 
described for mosquitoes (Helson et al. 1979b; Thorsen et al. 
1979), sentinel chicken flocks (Helson et al. 1979a), wild birds 
(Dorland et al. 1979), horses (Artsob et al. 1979), and humans 
(Mahdy et al. 1979). 



60 



5. CRITERIA FOR CONTROL 
a. Western Equine Encephalitis 

The objective of arbovirus surveillance programs is to 
predict the risk of transmission of virus to the human population 
in time to implement effective remedial action. Remedial measures 
continue to focus on suppression of vector population abundance, 
primarily by chemical control as part of integrated pest 
management programs. However, authorities relying on current 
vector control strategies are facing increasing opposition to 
pesticide use because of the environmental and public health 
implications of adulticiding, and, with respect to WEE, scepticism 
over the effectiveness of adulticiding in reducing human 
infections . 

McLintock (1976) described conditions necessary for an 
outbreak of Western Equine Encephalitis (WEE) to occur. 

1. There must be susceptible population. For WEE as well as SLE, 
horses and humans are susceptible populations. Rural residents 
are more at risk than urban ones (in Reisen and Monath 1988, Eadie 
and Freisen 1982) . 

2. The virus must be available to the mosquito vector. Infected 
passerine birds are the most important source of virus for the 
mosquito. Since the life cycle of WEE virus is not fully known 
(see DISEASES, 2a; VECTORS 3a), the precise role, as reservoirs, 
of birds and mammals from which virus isolations have been made is 
not well understood. Horses and humans, on which infected 
mosquitoes feed after fledgling birds are no longer readily 
available as hosts, are normal hosts of mammophilic mosquitoes 
infected with the virus. 

3. Populations of mosquito vectors must be sufficiently large to 
sustain an epidemic. Cx. tarsalis is the only species known to 
transmit WEE virus to humans and horses. 

Surveillance programs monitor parameters leading to the 
second and third of these conditions. The first condition is 
taken into consideration in determining control strategy. 
Criteria developed by the Manitoba Arbovirus Surveillance 
Committee were used to assess risk to public health in Manitoba 
and were also used in decision-making on emergency aerial spraying 
of municipalities. They were based on data collated by McLintock 
for Saskatchewan, and experience gained in Manitoba since the 1975 
outbreak. 

Prior to 1981, the criteria were not precisely defined 
because of a lack of an adequate database. Following criticism 
and review of its handling of the 1981 outbreak, Manitoba Health 
attempted to devise more rigorous criteria using four indices. 
However, these criteria were not followed consistently in 1983, 
the next period of increased viral activity and a subsequent 
outbreak. 

Assessment of risk was patterned after the surveillance 
programs in Saskatchewan and California (Walsh 1985) and were 
developed by comparisons between outbreak and non- outbreak years. 
The Manitoba Arbovirus Surveillance Committee developed thresholds 
of risk based on trap data, incidence of seroconversion in 

61 



sentinel flocks, and incidence of equine cases. Thresholds were 
based on trap distribution and collection regime and reporting 
procedures used 1976 - 1981 (Brust 1982, Wong and Neufeld 1982, 
Sekla and Stackiw 1982) . In both risk assessment and decision- 
making on control measures, indications in neighbouring 
jurisdictions were also considered. 

Comparison of criteria between jurisdictions is difficult 
because of differences in surveillance programs, e.g., in trapping 
schedules, handling and storage of samples, climatic differences, 
in addition to differences in species or strains of vectors , 
virus, or hosts. There are also considerable differences in 
attitude to risks to public health and approaches to protecting 
public health (see SURVEILLANCE, 4a). 

The surveillance and decision-making processes in Manitoba 
led to the declaration of four public health emergencies, for each 
of which a wide scale emergency aerial spray program was carried 
out. The criteria used are the basis for this discussion. 

Weather 

Climatic factors used to predict outbreak conditions include 
temperature, rainfall, soil moisture conditions of the previous 
fall, winter temperatures, amount of snow and rate of snowmelt. 

Temperatures are monitored to predict potential of virus 
multiplication in Cx. tarsalis and other mosquitoes, and on the 
rate of growth of mosquito populations. McLintock (1948) 
described two conditions of temperatures necessary for WEE 
outbreaks in the prairies : a mean average weekly temperature above 
normal during the last two weeks of June, and average mean weekly 
temperatures in July and August at least 2 C above normal. The 
second condition was not met in Manitoba in 1975 (Fraser and Brust 
1976). 

In an attempt to forecast population abundance of Cx. 
tarsalis in southern Manitoba, Raddatz developed a model for Cx. 
tarsalis populations of Winnipeg, based on the City of Winnipeg's 
NJLT collections 1977 - 1981 (Raddatz 1982). The model, based on 
temperature and rainfall conditions and still requiring 
confirmation, offers prediction eight weeks in advance of high 
Cx. tarsalis counts. A warm and wet late April and early May is 
required for the rapid increase of Cx. tarsalis populations in 
late June/early July, an increase necessary for an outbreak. 

In the United States, a computerized weather monitoring 
program (IPM program) is being developed. The Raddatz (1985) model 
is an encouraging first attempt for Canada, but until it is 
adequately tested, it remains an experimental tool. 

Winter temperatures, snow fall, and soil saturation levels 
are early season environmental conditions used to assess outbreak 
potential. These early season factors provide only secondary 
qualitative information. Impacts of snowfall and soil saturation 
levels are indicative of abundance of breeding sites, and in 
themselves are insufficiently direct to provide reliable 
predictions of virus activity. 

Winter temperatures affect population abundance of 

62 



overwintering adults. Survival of overwintering populations, 
including Cx. tarsalis , is inversely proportional to mean maximum 
winter temperature. Successful emergence is proportional to mean 
monthly temperature in late spring and abundance of females 
entering hibernation the previous fall (Eldridge 1987b) . Rapid 
increase in temperature and consequent melting of the snow pack 
lead to high populations of Cx. tarsalis (Reisen and Monath 
1988). These conditions also lead to high populations of Cs . 
inornata which are assummed to have a significant role in the WEE 
cycle in early spring and late fall. In California, river 
flooding is associated with high populations of Cx. tarsalis , but 
has not been a consideration in development of criteria for risk 
assessment in Canada. 

Weather preceeding arrival of migratory birds is critical 
for the development of outbreak conditions (Eldridge 1987b) . 
When local Culex populations have emerged from hibernation by the 
time migratory birds arrive, they are exposed to available virus 
in infected migrants. Adult mosquito populations active at the 
critical time period make an outbreak possible. SLE was 
introduced into Ontario in the spring of 1975 by migrating birds 
which are viremic for only 3 days . Time of emergence of 
overwintering Cx. tarsalis populations is determined by 
temperature (Eldridge 1987b) ; survival of emerging populations is 
also dependent on adequately high temperatures and adequate 
rainfall to support a breeding population. 

In Manitoba, Cx. tarsalis does not emerge early enough to 
feed on northward migrating birds. Birds migrate north in April; 
Cx. tarsalis females typically are not trapped in Manitoba or 
Saskatchewan until the second or third week of June . 

Abundance of Culex tarsalis Populations 

Criteria for the assessing risk on the basis of mosquito 
abundance in Manitoba were developed from monitoring carried out 
using standard light traps and flock traps since 1976. Two basic 
trap types were used: flock traps and New Jersey Light Traps 
(NJLT) . A third trap type, the CDC style carbon dioxide-baited 
trap, was also used also provide an indication of mosquito 
abundance because these provide large numbers of mosquitoes for 
viral analysis. Their value as indicators of abundance was 
restricted by an inadequate database on their trapping 
characteristics in Manitoba. 

Four species of mosquitoes were monitored in Manitoba; Cx. 
restuans , Cs . inornata, and Ae. vexans as well as Cx. tarsalis . 
In Saskatchewan, additional Aedes species are monitored. Only Cx. 
tarsalis is included in criteria for assessing risk of outbreaks. 
All selected species were tested for virus infection. 

Trap catches were interpreted on the basis of trap type, 
frequency of trap catch collection, number and location of trap 
sites, and meterological conditions over the trapping period. 
Because mosquito activity varies widely with ambient conditions, 
trap counts also vary widely with ambient conditions (Bidlingmayer 
1985). Hence, whenever possible, daily catches of mosquitoes were 

63 



made. However, because of limited resources, trap catches were 
made at lower and various frequencies: 1 (for distant sites), and 
2 , or 4 times weekly, depending on distance from Winnipeg. 

Flock Traps 

Flock trap design and use is described in Wong et al. 1976, 
and Wong and Neufeld 1982. Initially five, and after the 1979 
outbreak, eleven flock traps were used. Flock traps do not 
collect as many mosquitoes as light traps. Nevertheless, from 
data collected 1976-1981 on one flock trap and one suction style 
NJLT at each of five rural locations, Brust (1982) concluded that 
flock traps provided the most efficient indication of risk; flock 
trap catches showed increases in Cx. tar sails populations one to 
two weeks earlier than NJLT catches (Brust 1982). 

During years when human infections occurred, flock trap 
catches exceeded 75 female Cx. tarsalis /trap/week and Cx. 
Carsalis exceeded 38% of the total catch of mosquitoes. In non- 
outbreak years, Cx. Carsalis counts were less than 20 
females/trap /week, and less than 25% of the total flock trap 
catch. In outbreak years, Cx. Carsalis populations increased 
rapidly before mid July. High population abundance of Cx. 
Carsalis by mid July are apparently needed for virus 
amplification to build up to outbreak levels. In outbreak years, 
Cx. Carsalis numbers increased rapidly in flock traps during the 
first two weeks in July or earlier: greater than 10 Cx. Carsalis 
/trap night for three consecutive nights by the end of the second 
week of July, and 20-30 Cx. Carsalis or more /trap night during 
the second and third weeks of July for three days of longer. 

Light Traps 

Light traps give an index of relative mosquito abundance and 
provide greater numbers of mosquitoes for viral analysis. New 
Jersey style light traps, modified ("suction style") for 
livetrapping (Brust 1982) , were equipped with 100 watt bulbs 
rather than the standard 25 watt bulb in order to increase the 
number of mosquitoes caught for viral analysis. Only one NJLT 
was used per location, and at only 5 locations across the 
province. 

NJLT counts of Cx. Carsalis are also higher in outbreak 
years but the correlation between higher NJLT counts and outbreak 
years is less than that between flock trap counts and outbreak 
years (Brust 1982) . Again, counts of Cx. Carsalis in NJLT 
catches of three or more/trap night by the end of first week in 
July, and more than 10% of the total catch during the fourth week 
of June to mid July is also indicative of an outbreak. 

Cx. Carsalis counts in light traps exceed those in flock 
traps toward the end of the season. In Saskatchewan, survival of 
the overwintering population is estimated on NJLT catches. 
Emergence of hibernating females in spring is determined by light 
trap catches. If no females are caught before the first males, 
the hibernating population was small and survival also small. 

The City of Winnipeg has maintained a network of New Jersey 

64 



style light traps as part of its annual mosquito control program. 
The trap network has been operated for over a decade and now 
provides a useful database on mosquito population abundance . The 
City has developed a threshold of Cx. tarsalis abundance based on 
nightly average trap catches to predict risk of human infection 
(Dr. R. A. Ellis, pers comm.). An average of 50 or more female 
Cx. tarsalis /NJLT/night is predictive of an outbreak. 

Carbon Dioxide Baited Traps 

CDC style light traps baited with carbon dioxide were used 
in 15 sites across the province between 1982 -1985. The sites 
were chosen on the basis of human population and history of virus 
activity. Three traps were used per location to reduce effects of 
local and ambient conditions on trap efficiency. C0 2 -CDC trap 
catches were usually consistently higher (e.g. an average of 
approximately 75% greater numbers of Cx. tarsalis /trap/night in 
1983 in sites where flock traps were high). However, since C0 2 - 
CDC trap data are available for only one outbreak year (1983), the 
data are inadequate for development of predictive thresholds. 

Following the 1983 outbreak, thresholds of risk of 'low', 
'medium' , and 'high' of mosquito activity were determined by 
both flock trap and light trap catches (average number of females 
caught/trap/week) . Greater emphasis was placed on numbers rather 
than on relative abundance of Cx. tarsalis trapped and on 
abundance of Cx. tarsalis at critical times during the season. 

Virus Activity 

Virus activity was monitored using three parameters: virus 
isolations from mosquitoes, seroconversion in sentinel flocks, and 
incidence of horse infections. Virus isolations from mosquitoes 
were usually made each year, however, the rate of infections 
among mosquito pools differ between outbreak and non- outbreak 
years. During 1975-1981, less than 2% of pools of all mosquitoes 
species tested were positive in non outbreak years as compared 
nearly 5% or greater in outbreak years. Pools of Cs . inornata 
and Ae. vexans , and less frequently, Cq. perturbans , Ae. pionips , 
and An. earlei, were among those from which WEE virus was 
isolated. The rate of virus isolation from Cx. tarsalis pools 
was consistently greater in outbreak years: 8.5% or more of Cx. 
tarsalis pools with positive whereas the virus was not found in 
any Cx tarsalis pools in non-outbreak years (Sekla and Stackiw 
1982). 

Sentinel Flocks 

Sentinel flocks are a widely-used, valuable indicator of 
virus activity because they become infected when rate of epizootic 
transmission is high, and the virus is carried over from wild 
passerine hosts. When bled biweekly, sentinel flocks frequently 
provide seroconversion data prior to the onset of equine infection 
(Hess and Hayes 1967) , a situation that was usual in Manitoba but 
did not occur in 1983. 

In Manitoba, sentinel flock data gathered between 1975 and 

65 



1981 were consistent in distinguishing outbreak years from non- 
outbreak years, although the trapping system was varied in trap 
number, design, and location; types of birds; bleeding and 
exposure schedule (Wong and Neufled 1982). In non-outbreak years 
over the period of 1975 - 1981, the percentage of birds which 
seroconverted ranged from a low of less than IX to 3.3%. In 
outbreak years, the percentage which seroconverted was 16% , 26% 
and 84% (Wong and Neufled 1982). 

Equine Cases 

Horses are very sensitive to WEE infection, and are a useful 
sentinel animal for WEE virus activity. Diagnosis of WEE 
infection in horses is by serological confirmation of a rise in 
antibody titre, or a positive single serum sample (Neufeld and 
Nayar 1982) . Onset of equine cases in most epidemics has usually 
occurred two weeks before human infections (Hess and Hayes 1967). 
In all but one of the recent outbreaks, the first horse cases 
preceded human infection by two (1975, 1977) or three (1981) 
weeks. In 1983 no horse cases were reported until after the 
declaration of a health emergency, and the initiation of an aerial 
spray program. A rate of new cases of six or more per week for 
two consecutive weeks is predictive of an outbreak (Neufeld and 
Nayar 1982). 

An effective vaccine is available for horses . Not all 
horses are vaccinated, and some of those that are may still 
contract the disease. Young and therefore unvaccinated animals 
are particularly susceptible to virus infection. Use of equine 
cases as sentinels is compromised because the prevalence of 
vaccination of horses is not known. Only relative and indirect 
information can be gained from estimates of vaccine sales. 

Human Infection 

Monitoring of human cases is carried out to determine 
prevalence of WEE disease. Incidence of human cases is not an 
efficient predictive parameter. Human infections do not offer an 
early warning system. Infected humans show a variety of clinical 
symptoms which develop over at least eight to ten days, and often 
longer periods. Some cases go undetected until after the outbreak 
has been fully realized. Hence by the time human infections are 
diagnosed, the human population has already been at risk for , at 
least, eight to ten days, and perhaps considerably longer. 

Other Factors 

When indicators show departures from non- outbreak 
conditions, other factors tend to be considered in addition to 
defined criteria. These other factors include epidemiological 
features, previous experiences of disease outbreaks, and, 
following declaration of health emergencies, selection of target 
populations for control measures. In Manitoba and the bordering 
States, the Red River Valley area is considered to be at greater 
risk than western parts of the province, because historically, 
most indicators have occurred in the Red River Valley. The Red 

66 



River Valley location has not incorporated into criteria for 
assessing risk, but was considered when assigning priority for 
aerial spray treatment during outbreaks. 

Risk Assessment and Actionable Thresholds 

Thresholds of risk are based on a combination of 
environmental and epidemiological conditions encountered during 
the season which are favourable to high levels of mosquito 
production, and high levels of virus activity. 

Low Risk - Non-Outbreak Conditions 

Temperatures normal or below normal levels; precipitation 
(snowfall and spring rainfall) at normal or below normal levels; 
Vector population abundance at normal or below normal levels ; No 
virus isolations from vector populations ; Less than 4% rate of 
serconversion in sentinel flocks; No or occasional equine 
infections . 

Action Response 

Maintain routine monitoring. 

Medium Risk 

Above normal levels of up to four of the indicators . 
Greater level of risk if flock trap data or equine cases approach 
high risk level and with increasing number of indicators 
approaching high risk levels. 

Consideration of all parameters is essential since any 
parameter in itself is not indicative of an outbreak. Mosquito 
populations can be high; but not support virus transmission 
(Reeves et al. 1961); and the virus can be present in the absence 
of high mosquito populations as is demonstrated by both horse 
cases and seroconversion in sentinel flocks in non- outbreak 
years . 

Action Response 

Increased frequency of trap collection, increased frequency of 
sentinel flock bleeding, reminders to veterinarians for closer 
scrutiny of possible horse infections, information exchange with 
neighbouring jurisdictions and local mosquito control authorities, 
close monitoring of weather reports, soil saturation levels, flood 
forecasting, preliminary advisory to senior health officials. 

High Risk - Epidemic Situation 

Mean weekly temperatures over the last two weeks of July and 
average mean weekly temperatures in July and August at least 2 C 
above normal. Wet and warm April and May. 

Trap collections of 75% or more Cx. tarsal is /flock. 
trap/week, and 35% or more of total trap catch of Cx tarsalis . 
Fifty or more female Cx. tarsalis/ trap/week in NJLTs. 

Virus activity levels resulting in 8.5% or more of Cx. 
tarsalis pools positive and a rate of 20% or greater 
seroconversion in sentinel flocks. 

67 



Equine infections occurring at a rate of six new equine 
cases or more per week. 

Occurrence of human cases is the primary criterion for 
implementation of control measures. 

Action - Advisory to Minister of Health 

Risk of outbreak was assessed on objective scientifically 
developed criteria. However, the same type of criteria are not 
available for determining both what remedial measures should be 
implemented, and where emergency (aerial) spraying should be 
carried out, if spraying is the chosen course of action. 
Selection of targets for emergency aerial spraying has been by 
size of population centre, despite the fact that WEE is primarily 
a rural disease, and if available, surveillance data. When 
aerial spraying has been adopted as a control strategy the 
procedure of systematically spraying all municipalities, priorized 
according to population size, has been used. It provides an 
objective device for selecting targets. In 1983, the U. S. Centre 
for Disease Control recommended to the Minnesota Arbovirus 
Surveillance Committee that ULV using malathion be implemented, 
and that the decision to spray areas should be made on the basis 
of population size and data on virus activity and infection. In 
the 1983 emergency program in Manitoba, some municipalities were 
sprayed which were both distant from surveillance sites and which 
had no earlier record of WEE activity. 

More reasoned criteria for selecting sites for emergency 
aerial spraying are needed; lack of them are a deterrent to the 
implementation of a control option that can be carried out 
rapidly, on a wide -scale. 

Criteria for control should also be developed to include 
cost-benefit of methods employed, i.e., compare the cost of impact 
of the disease the public, and costs of control procedures and 
surveillance against benefit of reducing human suffering and 
impact of disease and control measures on livestock and wildlife. 

b. St. Louis Encephalitis 

Following the only reported outbreak of St. Louis 
encephalitis reported for Canada, in Ontario in 1975, a special 
document was prepared by the Committee on Programs for the 
Prevention of Mosquito -borne Encephalitis (Mahdy et al. 1979), for 
the Ontario Ministry of Health. In that report, MacKenzie (1979) 
described, in detail, mosquito control efforts related to St. 
Louis encephalitis in Ontario. 



68 



6. CONTROL OPTIONS 

a. Vector Suppression 

The mosquitoes carrying encephalitis virus from wildlife 
sources to people are the weakest link in the virus transmission 
cycle. Controlling the mosquito vector breaks that transmission 
chain and reduces the chances of people becoming infected with the 
virus. Thus, during epidemics of mosquito-borne encephalitis, 
every attempt possible is usually made to reduce the mosquito 
vectors that may be involved in virus transmission. 

There are many reference works available on mosquito vector 
control. However, most of these guidelines, although very 
helpful, are not directly transferrable to the Canadian situation, 
having been written, in most part, for conditions in other 
countries (e.g. Anon. 1976, 1978, 1982, 1987, 1989; Monath 1980). 
Provincial mosquito control guidelines also may be very useful, 
particularly for starting the mosquito larviciding operations they 
usually emphasize (e.g. Brust et al . 1976). Also, reference can 
be made to an unpublished, 3 -part technical manual on WEE 
surveillance and control in Manitoba (Ellis 1982a, b,c). In 
addition, a review of some of the papers describing the past 
emergency vector control programs in Manitoba and Ontario (e.g. 
Ellis 1976; Brust and Ellis 1976; MacKenzie 1979; Sekla 1982) 
would be useful. 

Mosquito vectors can be controlled, under Canadian 
conditions, in both larval and adult stages. Generally, it is 
considered impractical to attempt to control mosquitoes in the egg 
stage and no insecticides are available in this country for pupal 
mosquito control. The only registered mosquito pupicide, Flit 
MLO*, is no longer marketed in Canada. Thus, the choices are 
limited to mosquito larvicides and adulticides. Neither approach, 
mosquito larviciding or mosquito adulticiding is 100% effective. 
But, mosquito control can reduce the vector population and the 
chances of virus transmission. 

Depending upon the timing of the encephalitis outbreak, one 
may carry out both mosquito larviciding and adulticiding or only 
mosquito adulticiding. When it is late in the mosquito season 
(i.e. after mid- August) and most, if not all, of the Culex larvae 
present will be giving rise to adult mosquitoes that will be 
entering diapause rather than blood- feeding, medical -veterinary 
entomologists usually will recommend that control efforts be 
concentrated on those mosquito adults that are already present and 
possibly infective. Such a mosquito adulticiding program is aimed 
solely at breaking the virus transmission cycle without concern 
about the next year's population. The decision would have to be 
based on a thorough assessment of the percentage of female 
mosquito vectors that had entered diapause. 

Even late in the mosquito season, some workers might argue 
that both control options - mosquito larviciding and mosquito 
adulticiding - be taken because some of the newly- emerged 
mosquitoes may blood- feed, at least once, and, perhaps, carry the 
virus over the winter into the subsequent season. They might also 

69 



argue that the public would perceive a new mass emergence of 
mosquitoes, even of a non-vector species, as a general failure of 
the vector control program and become sceptical of both the 
disease control efforts and the effectiveness of mosquito adulti- 
ciding. 

If human cases were the only warning that a outbreak was in 
progress and those cases were not confirmed until late August, the 
best decision might be not to attempt any vector control. Without 
early indicators of virus and vector activity (i.e. an extensive 
surveillance program, including monitoring virus activity in 
sentinel flocks and mosquito vector population levels) , an 
outbreak may be well advanced before it is recognized. In such a 
circumstance, personal protection (including repellents, screened 
doors and windows, wearing proper outer-wear, avoiding mosquito- 
infested areas, etc.) might be the best (and only) course of 
action. Typically, there is sufficient time, once an imminent 
outbreak is recognized, to initiate vector control operations. 
Given even a basic vector and virus surveillance program, there 
may be a 2-4 week period during which vector control is possible. 
During this period and under optimum weather conditions, the 
vector population may increase while the virus amplifies in 
wildlife, resulting in many more human cases. Thus, the emergency 
mosquito control measures must not be delayed or their impact on 
the vector population will be greatly diminished. 



i. Non-chemical 

Ideally, mosquitoes could be controlled using non-chemical 
methods (Anon. 1965, 1977). Water management, in some 
jurisdictions, has been used successfully to maintain mosquito 
populations at acceptable levels. Saltmarshes, sewage and dairy 
lagoons, storm water-retention ponds, and even farm dug-outs can 
be managed to make them unsuitable for mosquito breeding through a 
combination of design, water level manipulation and vegetation 
control. 

To a lesser extent, open ditches along road, rail and 
transmission line rights-of-way also can be managed to minimize 
mosquito breeding. Properly designed, so that they drain quickly 
rather than retain run-off water, and regularly maintained, so 
that sediments are removed and vegetation is kept low, such 
ditches do not have to be major sources of mosquitoes. However, 
good ditch management methods are very expensive compared to 
conventional mosquito larviciding, especially in the relatively 
flat land areas of the Canadian prairies. 

Also, the public can be educated, over time, to recognize 
the importance of keeping private property free of water- filled 
containers. Leaf -plugged eavestroughs, discarded tires, buckets, 
bird baths, etc. that are full of stagnant water can contribute to 
neighbourhood mosquito problems. All of these various means of 
mosquito source reduction should be encouraged. 

Biological control Is another non- chemical alternative for 
mosquito control. The mosquito's natural enemies (including 

70 



pathogens, parasites and predators) could be used more effectively 
against mosquitoes in their various life stages. Some successes 
have been reported in the southern U.S.A., especially the use of 
mosquito-eating fish. However, although mosquitoes have many 
natural enemies and these organisms undoubtedly have some impact 
on mosquito populations, they rarely maintain mosquitoes at 
acceptable levels. They have to be manipulated by man if they are 
to work effectively. 

Only mosquito pathogens, particularly bacteria, have been 
successfully managed. Bacillus Churingiensis israelensis and 
Bacillus sphaericus have both been commercialized for larval 
mosquito control. Both bacteria can be mass-produced, packaged, 
shipped and stored for use. In the U.S.A., both bacteria are 
registered under several product brands. In Canada, only BTI is 
registered as a mosquito larvicide. The early larval instars are 
most susceptible to this bacteria. It has little effect on 4th- 
instar larvae. Thus, it requires more understanding of mosquito 
biology to be used successfully. Although some argue that BTI is 
not truly a biological control agent because it is a complex 
chemical within the bacteria that actually kills the mosquito, BTI 
is a natural pathogen of mosquito larvae and it is certainly not a 
conventional chemical larvicide. Its use should be encouraged in 
on- going mosquito larviciding programs across Canada. 

As much as these non- chemical means of mosquito control 
should be the basis of long-term mosquito abatement programs, they 
are of little value when one is faced with mosquito vector control 
after an outbreak of mosquito -borne encephalitis has been 
perceived. 

ii. Use of Insecticides 

To deal with vector control during an outbreak of mosquito- 
borne encephalitis, there is currently no alternative to the use 
of conventional chemical insecticides. The only choices are which 
mosquito larvicides and/or adulticides to use, given the time, 
personnel and spray equipment available and the product label 
restrictions. The alternatives should be examined carefully, 
considering their cost, effectiveness and environmental 
acceptability. 

Types and strategies 

Mosquito control - whether it be larval or adult mosquito 
control - can be carried out using ground-based and/or aerial 
application equipment (Anon., 1974). From the ground, the 
sprayers may include manual or powered back-pack sprayers and 
truck- or trailer-mounted power sprayers. From the air, either 
rotary- or fixed-wing aircraft can be used to apply the 
insecticide. The insecticides may be applied as coarse or fine 
mists, as dusts or granules or as thermal or cold aerosols. 
Product choice depends on what spray equipment is available, 
whether larviciding or adulticiding is planned, and whether or not 
sufficient insecticide can be procured in the time available to 
meet emergency requirements . 

71 



If an encephalitis outbreak is recognized early, mosquito 
larviciding may play an important role in preventing virus 
transmission. However, destroying the adult mosquito, a portion 
of which is carrying the virus from its first blood-meal, always 
must be the highest priority. 

Larviciding 

Mosquito larviciding is the introduction of biological or 
chemical insecticides into those aquatic habitats where mosquito 
larvae are believed to be present. Whether the larvicide is a 
biological material (e.g. the bacteria, BTI) or a chemical 
material (e.g. the organophosphate , Chlorpyriphos) , the aim is to 
destroy the larvae before they emerge as adults and disperse 
throughout an area. It is much easier to destroy a million 
mosquito larvae in 1 km of roadside ditch than to destroy the 
resulting adult mosquitoes which may spread out over a 100 square 
km area. Also, it is usually more economical and environmentally 
acceptable to destroy mosquitoes in their immature stage. 

If a decision is made to include mosquito larviciding in an 
emergency mosquito vector control program, it should be carefully 
planned and carried out. To have a significant impact on 
subsequent virus transmission, the larviciding program must be 
done as efficiently as possible. The spray equipment that is to 
be used must be already available or must be easily procured or 
hired. 

Large truck-mounted sprayers should be used to treat major 
roadside larval breeding sites in and around urban and rural 
population centres. Rotary-or fixed-wing aircraft should be used 
to treat larger breeding sites (e.g. flooded woodlots, sloughs, 
wide drainage ditches) . Helicopters are usually preferred over 
fixed-wing aircraft because of their greater manoeuvrability over 
smaller, off-road, breeding sides and their ability to land and be 
re-loaded quickly on farm access roads. 

The ground and aerial larviciding programs must be 
coordinated and mobile. Ideally, the ground-based spray equipment 
and operators and the aerial spray crews will be under the super- 
vision of an experienced mosquito abatement official with the 
authority and responsibility to larvicide in and around areas of 
highest priority based on larval surveys. The larviciding 
operation will, of necessity, have to be radio -equipped for good 
communications . 

Both the ground and aerial operators would work in concert 
with each other, crews travelling from town to town as 
surveillance indicates the need for controlling vectors in the 
larval stage. 

Also, "walk- in crews", equipped with motorized back-pack 
sprayers, could be used to treat small, off -road breeding sites 
that are either too small or too hazardous to treat using aircraft 
(e.g. small breeding sites located under transmission lines, 
between buildings or in backyards). 

Such an emergency mosquito larviciding operation could be 
made to work efficiently, given proper supervision and authority. 

72 



Its weakness is, of course, the likelihood that ground-based 
sprayers of the type used in mosquito control will not be 
available locally. Although helicopter spray crews and 
insecticide can be hired and procured fairly readily, or seconded 
from other provinces, it may take weeks or months to receive major 
spray equipment (e.g. Buffalo Turbine liquid- granular sprayer; 
John Bean mist-blower) ordered from U.S. manufacturers. Even a 
large, urban centre with an established mosquito abatement program 
rarely would have enough spray equipment to handle its own needs 
let alone be able to allow that equipment to be seconded. 

Thus, an emergency mosquito larviciding program may be 
limited to an aerial application program, any ground-based 
equipment available restricted to the municipality fortunate 
enough to have it. Nevertheless, the aerial larviciding program, 
using helicopters and crews under contract, could make a 
significant contribution to the overall vector control program. 

In an emergency situation, conventional chemical larvicides 
would be recommended. Biological larvicides (i.e. BTI) would not 
be acceptable because they are only effective, consistently, 
against 1st- 3rd instar larvae. Most larval breeding sites 
containing populations of vector species would have a mixture of 
eggs, all larval instars, and pupae. Thus, one would choose an 
insecticide that would kill all larval instars and remain in the 
water for as long as possible, killing larvae that subsequently 
hatch. One insecticide having these qualities and formulated as 
both a liquid for ground-based sprayers and as a granule for 
helicopter application is chlorpyriphos . Others are listed in the 
Appendix. 

Adulticiding 

Mosquito adulticiding is the application of insecticides to 
destroy adult mosquitoes. It may involve "space spraying" which 
is the release of thermal or cold aerosol droplets into the air or 
"residual spraying" which is the application of a coarse liquid 
spray to vegetation where mosquitoes rest. Mosquito adulticiding 
(especially space spraying) has little effect on larval mosquitoes 
and they will continue to emerge as adults . 

Space spraying may be accomplished with thermal or cold 
foggers, carried by hand, truck or aircraft. The small droplets 
that are generated by the sprayers drift through mosquito- infested 
areas, impinging on mosquitoes and killing them. After the 
droplets hit a surface and slowly evaporate or drift out of the 
target area, they no longer will kill mosquitoes. Thus, there is 
no residual carry-over of the insecticide. As a guide, as soon as 
the odour of the insecticide disappears from the area (usually 
within 1-2 hours) , there is too little insecticide remaining to 
kill mosquitoes. 

Space spraying is most efficient when done from the air 
(Akesson and Yates 1982). Ground-based fogging is obviously 
limited, except in large parks and golf courses, to areas 
immediately adjacent to roads, streets and lanes. The thermal or 
cold fog will drift downwind about 100 m before it begins to 

73 



dissipate. Aerial ULV applications are not restricted in this 
manner, allowing large blocks to be treated more -or -less uniformly 
with mosquito adulticide. Aircraft are also much more efficient 
than truck-mounted foggers . For example, one DC-6 spray plane 
equates to about 150 truck-mounted foggers and the area coverage 
is about 10 times greater. 

Many active ingredients are registered for use as space 
sprays for adult mosquito control. Some are limited to use with 
thermal aerosol generators (i.e. the old thermal foggers); others 
are registered for use in cold aerosol or ultralow volume sprayers 
(i.e. ULV or cold foggers). Some can only be used in ground- 
based equipment; others can be used in both ground and aerial 
spray equipment. Although there are several possible choices, 
only malathion and propoxur have been used in major emergency 
vector control programs in Canada. Both these products can be 
used from the ground or air and with either thermal or ULV 
sprayers. Each has its pros and cons but, at least, the problems 
with each are fairly well known and manageable. 

Residual spraying is more limited in that only those 
mosquitoes resting in or attempting to rest in treated vegetation 
will be contacted and killed by the adulticide. Because residual 
sprays are usually limited to application using ground-based spray 
equipment, the total area sprayed is limited to vegetation reached 
from roadsides. Further, some vegetation (e.g. many sensitive 
flowers and shrubs) will be adversely affected by such residual 
sprays (unless water-based or very weak emulsions) . 

However, residual sprays can be used to advantage in 
roadside ditches, killing resting adult mosquitoes and, possibly, 
mosquito larvae breeding in flooded portions of those ditches. 
Such sprays may also destroy newly emerging adult mosquitoes and 
adult female mosquitoes returning to these sites to lay their 
eggs. 

Many insecticides are registered in Canada as residual 
sprays for adult mosquito control. Those used most widely include 
chlorpyriphos and methoxychlor . Both would serve well during a 
health emergency, lasting 2-3 weeks on vegetation. Another 
alternative is Malathion. But, because of its short residual 
activity (lasting only a few days at best) , it is seldom 
recommended for vector control programs where the duration of 
residual activity must be 10-20 days. 

Comparison of Ground and Aerial Application 

As noted above, both ground and aerial application have 
their place in both routine and emergency mosquito vector control 
programs, in both the larviciding and adulticiding operations. 
For large-area treatments, especially for adult mosquito control, 
aerial applications are generally more efficient and economical 
than ground-based applications. However, in the case of mosquito 
larviciding, many vector breeding sites are small or occur in 
narrow roadside ditches and they are dealt with most effectively 
using truck-mounted or back-pack sprayers. 

Thus, assuming the resources were available, one would carry 

74 



out mosquito larviciding from both the ground and air. If ground- 
based larviciding equipment is not readily available, an aerial 
larviciding program should still be considered. Although many 
small breeding sites might be missed, the aerial spraying might 
have a major impact on the mosquito vector population. 

Large-area mosquito adulticiding is best carried out from 
the air during a health emergency. This mode of application 
provides for much quicker and more even coverage of an area with 
the adulticide at less cost than an incomplete, slower, ground- 
based operation. For example, under favourable conditions, a city 
the size of Winnipeg might be protected in one day using one 
large, multi-engine aircraft with an adequate insecticide load 
capacity. Under the same favourable conditions, it might take 10 
days for 10 truck-mounted foggers to treat the same area, omitting 
portions that were inaccessible by road. However, it should be 
remembered that aerial applicators may not necessarily be 
available during a health emergency. If this were true, even a 
slow, incomplete, ground-based, adulticiding operation would be 
preferable to nothing. 

In an ideal situation, one in which both ground and aerial 
application equipment is available, both types of equipment could 
be used to advantage in an emergency situation. The ground-based 
equipment may be mobilized faster and carry out mosquito 
adulticiding while the aircraft is being readied. Further, the 
truck-mounted equipment might be used, after the aerial 
application has been done and moved on to other areas, to "touch 
up" areas where either new adult mosquito emergences have occurred 
or areas where the level of control from the aerial application 
was unacceptable. Truck-mounted equipment could also be used to 
treat a series of small towns while the aircraft was used to treat 
larger centres. 

Control Requirements/Procedures 

Emergency vector control requires trained personnel, spray 
equipment and insecticide(s) . Ideally, each province which has 
had a history of outbreaks of mosquito -borne encephalitis will 
maintain an up-to-date inventory of the resources available to 
deal with possible future outbreaks. Knowing who and what is or 
can be made available is crucial to a rapid response to such an 
outbreak. 

Fortunately, most such provinces have ongoing mosquito 
abatement programs in some of their larger cities or regions. The 
staff involved in these programs can advise on what manpower and 
equipment they may have available to assist. From this base of 
experienced mosquito control officials, the province may be able 
to appoint someone to direct the emergency spray operations. In 
addition, these officials can suggest suppliers of needed 
insecticides either from within the province or nationally, 
through local sales offices, based on recent calls for insecticide 
tenders that they have made. 

Following their advice could save the province considerable 
money in purchasing insecticides. These people can give an 

75 



objective assessment of how the available insecticides perform 
locally and on the past service records of suppliers. These 
mosquito abatement agencies may also be able to supply needed 
insecticides, on a replacement basis, before the commercial 
suppliers can produce and deliver materials, enabling an emergency 
program to begin operation as early as possible. Similarly, major 
mosquito abatement agencies in adjacent provinces may be contacted 
for advice, and possibly emergency start-up supplies of materials. 

Two major considerations in large-area mosquito vector 
control programs are the insecticide to use and the contractor to 
hire for its aerial application. The insecticides currently 
registered in Canada for mosquito control, using aerial ULV 
application equipment, are propoxur and malathion. Both have 
environmental pros and cons but both have been used successfully 
in Canada for emergency vector control. Their most current unit 
costs and costs of application can be compared when an emergency 
occurs in order to determine which oe to use. 

When choosing an experienced aerial applicator with multi- 
engine aircraft, equipped with the specialized ULV spray nozzles 
required for vector control, the choices are more limited. Only 
one aerial application firm in Canada has experience with large - 
area, emergency mosquito vector control. Conair Aviation of 
Abbottsford, B.C., was the aerial applicator that carried out the 
emergency spraying in Ontario in 1975 and in Manitoba in 1975, 
1977, 1981, and 1983. 

One should expect local aerial application firms, usually 
small businesses with 1 or 2 ag-planes, each equipped with 
conventional boom and nozzle sprayers, to lobby for the aerial 
application contract. Local industry should be supported, all 
things being equal. However, it must be emphasized that having 
the proper equipment and experienced staff is most important. 

One DC- 6, with 2 crew members and having a 16,000 L 
insecticide capacity and equipped with the specialized ULV nozzles 
needed for its application, can treat 44,500 hectares in under 4 
hours. For small ag-planes to do the same work in the same time, 
one would need 69 ag-planes, 46 spotter planes, and a fleet of 
insecticide and fuel supply trucks. One should also consider that 
69 aerial applicator agreements would have to be developed. 

The most important consideration in selecting an aerial 
applicator is safety in the air. Perhaps, the best advice such 
lobbyists can be given is for them to acquire equipment and gain 
experience with non- emergency mosquito control. Some of them 
would then be in a position to assist in future vector control 
programs . 

Every effort should be made to contract with the suppliers 
of insecticide and aerial application services as soon as the need 
for emergency vector control is recognized. Even after these 
suppliers are designated, there will be many problems to solve. 

Relevant Provincial and Federal Legislation 

Many federal and provincial Acts and regulations relate, 
directly or indirectly, to routine and emergency mosquito vector 

76 



control operations. The federal Pest Control Products Act and 
associated regulations are, of course, the key concerns. 
Basically, the Act states that only registered insecticides may be 
used and then only in accordance with approved label directions 
and precautions. This should not present any problem in vector 
control programs but should certainly be followed. If any 
ambiguities are perceived, advice should be sought from the 
Pesticides Directorate of Agriculture Canada and followed. 

If migratory bird refuges are contained within proposed 
spray blocks , attention should be paid to the Canada Migratory 
Birds Convention Act, and close coordination maintained with local 
wildlife authorities. Generally, such refuges should not be 
included in emergency spray programs unless the risk to human 
health outweighs any possible risks to waterfowl and their 
habitat. 

Most provinces also have Acts and regulations governing the 
use of pesticides (e.g. Alberta Agricultural Chemicals Act, 
Manitoba Pesticides and Fertilizers Control Act, Manitoba 
Environment Act, Ontario Pesticides Act). Also, the provinces may 
each have several other Acts that indirectly affect pesticide 
applications (e.g. Environmental Assessment Acts, Workplace Safety 
and Health Acts, Transportation of Dangerous Goods Acts, etc.). 

Provincial regulatory officials should be consulted early to 
ensure that all applicable regulations under these Acts are either 
followed during routine mosquito control operations or, if 
necessary, waived for the duration of emergency vector control 
operations . 

iii. Aerial Insecticide Application 

Mosquito vector populations can be reduced fairly quickly by 
emergency wide-area aerial applications of insecticide. After the 
human population centres that are at risk from mosquito -borne 
encephalitis are identified, plans can be made to aerially spray 
these centres and an adequate area surrounding each of them. The 
centres may be identified by the occurrence of human cases, horse 
cases, sentinel flock virus activity and/or high vector 
populations. These centres may be priorized on the basis of human 
population levels and/or incidences of virus activity. 

Once known, detailed maps (usually the most current 
topographical maps that are available) for these cities and towns 
can be obtained and the spray blocks drawn onto them. Usually, 
there is only one spray block per small city or town and 3 or 4 
spray blocks per larger city. The spray block is centred over the 
population centre and includes a buffer zone of up to 10 km around 
the town or city. 

The topographical maps usually show the location of 
obstacles to low- level flight, including radio and television 
transmission towers, water towers, etc. Flight lines can be drawn 
to avoid these obstacles. The longitude -latitude coordinates 
given on the map can be used to set-up the computerized flight 
navigation equipment, ensuring precise start and finish points for 
each of the parallel flight lines within the spray block. 

77 



When the number of populated centres is known and the spray 
block maps have been developed, the total surface area to be 
treated will be known (although additional centres might be added 
after the spray operations begin) . Once the treatment area is 
known, the amount of insecticide required can be calculated and 
ordered. Also, based on the number of spray blocks and their 
size, negotiations can begin with the contractor on aerial 
application costs. 

Typically, there are fees associated with moving aircraft 
into the province, daily positioning fees at the airport, 
maintenance fees for holding the aircraft while awaiting 
acceptable weather conditions for spraying, and fees for the 
actual spraying. A fairly accurate picture of the costs as- 
sociated with the health emergency can be developed once the spray 
blocks are identified, the insecticide is ordered and the contract 
with the aerial applicator has been finalized. 

While all of this is happening, the emergency spray 
operations base can be set-up at the closest international 
airport, the public information centre can be organized, ground- 
support personnel can be arranged, legal matters can be attended 
to, surveillance can be accelerated, spray monitoring and 
evaluating procedures developed, reporting procedures agreed to, 
etc. 

One should expect that local environmental groups and 
individuals will attempt to stop the emergency spray operations. 
Reasons may vary but usually will centre on health and 
environmental concerns. Tactics may include media reports on the 
real and/or imagined effects of similar, past spray programs, 
attempted court injunctions based on harmful effects of spraying 
on the health of individuals or groups or the government's 
ignoring its own Acts and regulations. Everyone involved in the 
health emergency can expect to be affected by the challenges these 
tactics present. 

Matters may become somewhat chaotic as all the various 
agencies are trying to either organize themselves, ensure various 
federal and provincial regulations are being followed, fight legal 
battles, etc. Events are often further complicated because key 
decision makers are on vacation during late July and early August. 
However, once the usual start-up problems are overcome, the spray 
operations usually settle down to the business at hand. 

Weather Conditions 

The success of aerial ULV insecticide applications is 
closely tied to the weather conditions that occur during and 
immediately after spraying. Thus, meteorological data are needed 
for operational purposes throughout the duration of the emergency 
spray operations . These data not only determine when and where 
spraying will take place but also may be important in the 
monitoring of spray dispersal, the evaluation of vector mortality, 
the assessment of disease risk and the investigation of damage 
claims. Obviously, the full cooperation of the Atmospheric 
Environment Service is required. 

78 



Ideally, the aerial applications will be carried out when 
weather conditions and time of day favour both uniform insecticide 
droplet dispersal and mosquito flight activity. Realistically, 
weather conditions over a spray block must sometimes be 
extrapolated from nearby observation points and, because a spray 
flight may take 3 hours to complete, changes in weather conditions 
over the spray block can occur during the spray operation, 
whereas the person directing spray operations may make the 
decision to begin spraying, in consultation with meteorologists 
and the spray crew supervisor, the ultimate decision is made by 
the pilot. The pilot is responsible for the safe operation of his 
aircraft and may decide, on the ground, that the flight cannot 
take place for mechanical or other reasons or, in the air, that 
the flight be aborted for weather or mechanical reasons. 

Spraying should occur if the following weather criteria are 
met: i.e. temperatures of 12-28° C, relative humidities of 35- 
95%, wind velocities of 4 to 16 km/h, wind direction at an angle 
to the flight lines (the closer to perpendicular the better), and 
adequate light for visual flight. These criteria for spraying are 
difficult to meet. Each factor must be considered in relation to 
the others and a judgment call must be made. Frequently, the 
decision to begin spraying on a given evening or morning will be 
made at the last minute to take advantage of favourable weather 
conditions at any one of several possible spray zones. 

This last-minute decision-making, although unavoidable, 
often causes problems for personnel involved in informing 
officials and the public and monitoring the spray operation, 
underlining the need for good communications equipment and 
procedures. 

Environmentally-sensitive areas 

Environmentally- sensitive areas, over which direct spraying 
during a health emergency should be avoided, if at all possible, 
include those areas where there are large gatherings of people, 
outdoors during the actual spraying, and those areas which are 
truly environmentally-sensitive. Examples of the former include 
such recreational events as major football games in open stadiums 
and large, special weekend events in major parks. Examples of the 
latter include bird and other wildlife refuges and zoos where 
large assemblages of rare or endangered wildlife may be present. 

Adjustments to the spray block design must be made to 
account for some of the environmentally- sensitive areas if these 
occur on the periphery of the spray block. Otherwise, the spray 
can be turned off just before the aircraft flies over the area 
involved. 

Requests may be received to omit small areas for one reason 
or another (e.g., a hospital complex, a golf tournament) but it is 
impractical to turn the spray off for these areas . In the case of 
hospitals, food processing complexes, etc., maintenance personnel 
can be advised to close windows and turn off air conditioning 
equipment for a few hours. Small, recreational events can be 
postponed or cancelled if the organizers are concerned. 

79 



Routine mosquito control operations may also affect 
environmentally sensitive areas. The same precautions should be 
followed. Because routine operations involve smaller areas, at 
least on a day-to-day basis, many small but sensitive areas can be 
excluded from spraying, including buffer areas adjacent to persons 
registering their opposition to spraying. 

iv. Activity Periods of Vectors 

An adult mosquito vector control program must consider 
mosquito behaviour patterns. Host-seeking and dispersal flight in 
Cx. tarsal is peak between 30 minutes after sunset and midnight 
and at about 30 minutes before sunrise (Bailey et al . 1965; Nelson 
and Spadoni 1972) . Adults leave daytime resting sites when the 
light intensity decreases to < 30 lux and seek daytime resting 
sites shortly before sunrise, when light intensities increase to > 
80 lux (Gjullin et al. 1963). A variety of natural habitats (e.g. 
tall vegetation, wood lots, animal burrows) and artificial 
habitats (e.g. culverts, chicken houses and other farm buildings) 
serve as daytime resting sites (Mitchell et al. 1980). 

For maximum vector suppression, mosquito adulticiding should 
be conducted during the peak flight and host- seeking periods of 
the day. The most effective periods for adulticiding would be 
after sunset and prior to sunrise. Aerial adulticiding cannot be 
conducted during those times, as aviation regulations in Canada 
restrict low level flights over urban areas to daylight hours. 
Therefore aerial applications of ULV insecticides for vector 
control in urban areas have been made in the early evening hours , 
when temperatures are above 10 to 12 C and when wind speeds are 
below 16 km/h (Ellis 1976). Ground-based adulticiding, with ULV 
aerosol sprayers, is usually conducted from 2100h to 0500h, the 
period of greatest flight activity in host- seeking mosquitoes 
(Ellis 1976). 

When control of Cx. tarsalis is carried out to reduce the 
risk of human infection of WEE virus, it is important to determine 
when blood- feeding activity ceases and when populations prepare 
for overwintering. Because females overwinter as non-blood fed, 
nulliparous individuals (Blackmore and Dow 1962; Bennington et al. 
1958b; Burdick and Kardos 1963), with sufficient lipid reserves to 
last until spring (Kliewer et al. 1969; Schaefer and Miura 1972; 
Schaefer et al. 1971; Schaefer and Washino 1969, 1970), such 
females would not seek a blood-meal and would not be involved in 
virus transmission. 

Methods for assessing when diapause begins in Cx. tarsalis 
populations are not well defined (Buth 1983) . Measurements of the 
relative size of ovarian follicles and the germarium in females is 
one method of evaluation. When serial populations of a Manitoba 
strain of Cx. tarsalis were reared outdoors in Winnipeg, and 
adults maintained outdoors for 2 weeks, some females were in 
diapause by 27 July. By 9 August, 70 to 75% of the females were 
in diapause (Buth 1983) . Another indicator of diapause may be the 
rapid reduction in females coming to chicken shed traps and C0 2 
traps while egg rafts and immatures of Cx. tarsalis are abundant, 

80 



and nightly temperatures are considerably above the threshold for 
flight. The precipitous drop in numbers attracted to chickens 
during August 1981 (Brust 1982) and to C0 2 traps near Winnipeg 
during August 1985 and 1986 (Brust unpublished) would suggest that 
diapausing females of Cx. tarsalis are not being trapped. Similar 
reductions in Cx. tarsalis occur in light trap collections in 
Winnipeg during August (Raddatz 1985) . 

Light traps captured as many parous Cx. restuans and Cx. 
salinarius as C0 2 supplemented light traps (Magnarelli 1975; 
Feldlaufer and Crans 1979) indicating that light traps may be 
sampling mosquitoes in the same physiological state as those 
attracted to C0 2 traps. If this is so for Cx. tarsalis, it might 
explain the rapid drop in light trap catches at Winnipeg in early 
August 1979, at a time when weather conditions suggested trap 
collections should be increasing (Raddatz 1985) . 

The threshold light trap index of Cx. tarsalis necessary to 
transmit WEE virus to humans has not been determined for Manitoba. 
If isolations of the virus in Cx. tarsalis are made in mid- summer 
and the seroconversion rate in sentinel chickens exceeds 20%, an 
epizootic and an epidemic of WEE may occur (Wong and Neufeld 
1982). Before vector control is initiated on an emergency basis, 
assessments of parity and diapause rates in Cx. tarsalis should be 
determined. Several collection methods should be used to sample 
the vector population, and properly evaluate the risk of infection 
to humans . 

v. Honey Bee Activity 

An extensive review of the effects of pesticides on bee 
pollinators may be found in Johansen (1977) . Practical aspects 
that should be considered in mosquito control operations involving 
agricultural areas, and by beekeepers who may be affected by an 
insecticide application, are given by Atkins (1975) and McGregor 
(1976). The main factors are 1) honey bees may be foraging on 
flowering plants during all hours of the day, but primarily when 
temperatures are above 20 C 2) honey bees may be killed by direct 
contact with insecticide droplets during flight or while gathering 
nectar or pollen 3) the insecticide may be ingested with nectar 
or pollen, and kill as a stomach poison 4) bees may die in the 
field if the insecticide acts quickly, and bee death may not be 
observed by the beekeeper. With slow acting insecticides bees may 
return to the hive where they may die at the entrance or inside 
the hive 5) bees may forage 2 km or more from the hive, and 
beekeepers may suffer losses even if their hives are outside the 
target area 6) insecticide drift, especially from ULV 
applications may carry beyond the target area 7) the insecticide 
used should be selectively toxic to mosquitoes and should degrade 
as quickly as possible after mosquitoes are killed. 

When mosquito adulticiding operations are conducted in 
agricultural areas , honey bees foraging for nectar or pollen are 
at risk. Aerial ULV applications of propoxur and malathion 
(during 1981 and 1983, respectively) in Manitoba killed 
significant numbers of honey bees in all the treated areas of the 

81 



Province (Dixon and Fingler 1982, 1984). Direct losses to 
beekeepers in 1981, when propoxur was used, totalled $87,455. 
Honey bee and leaf cutter bee losses in 1983, when malathion was 
used, totalled $846,429. Beekeepers and leaf cutter bee operators 
were compensated by the Province of Manitoba for the loss of bees, 
and the estimated losses of honey and alfalfa seed production that 
resulted from the emergency vector control operation (Dixon and 
Fingler 1982, 1984). The greater losses in 1983 were due to the 
more extensive agricultural area within the treatment zone and the 
greater toxicity to bees of malathion compared to propoxur (Dixon 
and Fingler 1984) . 



82 



b. Host Protection 

Most female mosquitoes require a blood-meal in order to 
develop their eggs. The source of this blood is called their 
host. Preventing mosquitoes from biting an individual person or 
animal is termed host protection. Some people will argue that the 
best way to protect people and domestic animals from mosquito 
bites and mosquito -borne disease is host protection. Others will 
argue that host protection, although important, is only one 
component of protection from mosquito -caused annoyance and 
disease. 

Regardless, in certain situations, host protection may be 
the only means of relief from mosquitoes. Thus, this section 
attempts to describe the various alternatives that are available. 
Discussion is limited to the protection of humans and horses, the 
two hosts most likely to be seriously affected by mosquito-borne 
encephalitis viruses. 

i. Suitable Clothing 

People who must be outdoors while mosquitoes are active can 
minimize mosquito bites by wearing appropriate clothing. Loose- 
fitting, long-sleeved shirts, slacks, socks and hats reduce the 
skin surface area that is exposed. If this clothing is made of a 
thick, tightly-woven material, mosquito bites will be minimized. 

Because mosquitoes are more attracted to dark colours it 
helps to wear light-coloured clothing. Orange, yellow, beige, and 
pastel colours reportedly are among the least attractive colours. 
On the other hand, purple, navy-blue, brown, and other dark 
colours are very attractive to mosquitoes. 

Unfortunately, temperatures are often high during July and 
August when encephalitis outbreaks occur. People tend to wear 
shorts and t-shirts rather than the heavier clothing noted above. 
Sometimes, the use of such summer-wear may be balanced by applying 
repellents to this greater area of exposed skin. 

Some new light-weight, light-coloured, tightly-woven fabrics 
are being developed for people who spend considerable time 
outdoors. Marketed as "sun- screen" clothing, pants and jackets 
made of these materials may afford some protection from mosquito 
bites. Because of their tight weave, some of these synthetic 
materials do not breathe very well, causing a build-up of moisture 
inside and subsequent discomfort. However, for relatively 
inactive people, sitting outdoors, they may prove to be an 
alternative means of protection. 

II. Screening and Netting 

People can reduce their exposure to mosquitoes by using 
screens to prevent mosquitoes from entering their buildings, 
homes, mobile homes, tents, etc. Windows, doors, vents and other 
openings should be covered with mosquito -proof screening. 

Screens (16x16 or 14x18 meshes to the inch) to prevent 
mosquito penetration must be well maintained. Screens with holes 
or tears should be repaired or replaced before the mosquito season 

83 



begins. If a hole is present, some mosquitoes will find it. 

Because mosquitoes often will attempt to follow people 
indoors, screen doors should have fast-acting, automatic closing 
devices. Perhaps, the simplest such device is the old-fashioned 
spring-return. 

Infants in indoor cribs or outdoor carriages can be further 
protected by mosquito netting. A rectangular piece of thin, 
cotton or nylon material (23-26 mesh per inch) can be fastened 
over the crib or carriage to prevent mosquitoes from biting 
resting infants. Similar "bed nets" or "mosquito bars" could be 
made for campers resting in tents that do not have proper 
screening. 

Head nets may be used by older children and adults who may 
be sensitive to the use of repellents. Unfortunately, head nets 
are usually uncomfortable and awkward to wear, and consequently, 
are used only when mosquito annoyance levels are unbearable. The 
most comfortable are those that use a dark coloured netting, with 
14-16 meshes per inch. Often sold as bee veils for use by bee- 
keepers, these devices are an effective means of preventing bites 
on the head area. 

Air curtains can be used to prevent mosquitoes from entering 
loading and access doors (e.g., in commercial storage and 
maintenance facilities) where screening may be impractical. 
Ultraviolet insect electrocution traps, placed indoors, may be 
used to kill mosquitoes that are able to enter such buildings. 

Screened gazebos and porches are another means of minimizing 
mosquito bites while enabling people to enjoy their evenings 
outdoors . 

Related to this matter, some workers advocate applying an 
approved, residual insecticide to screen doors and windows and 
surrounding surfaces. Screens can be treated by using a paint 
brush to apply the diluted insecticide . 

iii. Behaviour Modification 

Because most mosquito vectors are most active during the 
periods of dawn and dusk, avoidance of human activity during these 
periods, especially in areas of high mosquito infestation, would 
reduce the frequency of human -mosquito encounters, and thus, the 
risks of disease transmission. 

Providing this basic information to the public, before and 
during an encephalitis outbreak, and encouraging them to schedule 
their recreational activities accordingly may afford some 
protection. Unfortunately, many people will either ignore this 
means of personal protection or are not in a position, for 
occupational (e.g. , farmers harvesting their crops) or other 
reasons, to follow these simple precautions. 

During an outbreak of encephalitis, public health officials 
should make every possible effort to motivate people, particularly 
those individuals who are in high risk categories (e.g., infants; 
farmers), to avoid exposure to mosquitoes. Suggesting that 
activities be carried out in open, sunny, windswept areas during 
the middle of the day rather than in heavily-vegetated, shady, 

84 



protected areas during the evening may reduce the risk of mosquito 
bites and possible disease transmission while recognizing the need 
for people to be outdoors during the mosquito season. 

iv. Topically-applied Repellents 

If mosquitoes cannot be avoided, one method of reducing 
mosquito bites is to repel them. Insect repellents applied to 
exposed skin disrupt the attacking mosquito's sensory organs, 
essentially confusing them and preventing them from biting. 

Repellents can be purchased in a variety of forms including 
liquids in squeeze bottles, pressurized spray cans, sticks, foams 
and wipes. They may be scented or unscented. Others may be 
formulated as combination repellents -sun screens. Also, many 
different active ingredients, alone or in combination, are used in 
repellents . 

The active ingredients most commonly found in repellents 
include the following: 

o Oil of citronella; 

o Citronyl; 

o N,n-diethyl-m-toluamide (DEET) ; 

o Dimethyl phthalate; 

o Ethylhexanediol ; 

o Oil of lavender; 

o Bisbutylene tetrahydro furfural (MGK R-ll); 

o Di-n-propyl isocinchomeronate (MGK 326) ; 

o N-octyl bicycloheptene dicarboximide (MGK 264) . 

DEET, alone or in combination with one or more of the other 
active ingredients, is the primary ingredient most commonly found 
in repellents. The per cent active ingredient present in a 
formulation may vary considerably from product to product. Given 
the bewildering number of choices available, people may be 
confused as to which repellent to buy (Appendix 1) . 

Some people choose to make and use their own mosquito 
repellent. Home-made preparations and remedies include animal 
grease, vitamin B12, lemon peels, oil of citronella, baby oil, 
bath oil, etc. Although some of these materials may provide some 
protection against mosquitoes, commercial repellents generally are 
more dependable. Those repellents having DEET as the primary 
active ingredient will provide an acceptable level of protection 
against mosquito bites. 

When repellents are applied to exposed skin, they usually 
can prevent mosquito bites for 2 hours or more, depending on the 
mosquito species involved, the numbers of mosquitoes present, the 
formulation used and the user's level of activity. Repellents are 
removed from the skin by absorption, evaporation, rain, sweating, 
swimming or wiping. Usually, repellents must be reapplied every 
few hours to maintain their effectiveness. 

Some repellents, in aerosol form, can also be sprayed onto 
clothing (e.g., socks, cuffs) to enhance their protection. 
Repellent applied to clothing usually will last longer than when 

85 



applied to skin. If people conscientiously use repellents while 
they are outdoors, in combination with other personal protection 
measures (e.g., suitable clothing), the risk of being bitten by 
mosquitoes will be reduced significantly. 

Repellents should, of course, be used carefully, following 
label directions. Many repellents are solvents, damaging paints, 
lacquers, varnishes, nail polish, and other plastic materials. 
Susceptible plastic materials may include watch crystals, eye- 
glass frames, golf clubs, helmets, telephones, furniture, seat 
covers, pens, and certain dynel-or rayon-based fabrics. 

Because personal repellents are applied to the skin, their 
safe use is very important. They should not, as a rule, be 
applied to infants or toddlers. An adult should apply them to 
young children, taking special care to avoid contact with the 
eyes, lips and nose. Older children should be instructed in the 
safe use of repellents. 

Aerosol repellents are best sprayed into the open hand and 
then rubbed onto the face and neck rather than spraying directly. 
They should not be sprayed near the mouth or eyes of humans or 
pets. 

Although very uncommon, some people may have an adverse 
reaction to a repellent. This may range from a short-term, 
allergic skin reaction to a toxic reaction such as generalized 
seizures. Ingestion of DEET may be fatal. Persons who are 
sensitive to known repellents should be especially careful. 
Excessive or prolonged use of a repellent, particularly by young 
children, should be avoided. 

If a slight allergic reaction to one repellent is 
experienced, switching to a repellent with a different active 
ingredient (e.g., from DEET to oil of citronella) may correct the 
problem. In case of a serious reaction, one should seek medical 
attention immediately. 

v. Repellent- impregnated Clothing 

Many people want to be or must be outdoors for extended 
periods of time while mosquitoes are active. As an alternative to 
the repeated, topical application of a repellent, some people have 
found repellent- impregnated jackets (usually hooded and with 
optional matching pants) to be an effective means of personal 
protection. The active ingredient used to impregnate the fabric 
is usually DEET or citronyl. Some manufacturers claim that such 
jackets will provide up to 32 hours of protection per charge. 

Typically, a light-weight, light-coloured mesh jacket is 
impregnated with repellent by placing it into a storage bag and 
adding 10-25 mL of repellent. After several hours, the jacket may 
be used. Most such jackets can be re-charged with repellent and 
used over and over. These jackets are popular among fishermen, 
campers, hunters, linemen, surveyors, farmers, photographers, 
lumberjacks, roughnecks, boaters, gardeners, golfers, and other 
outdoor workers . 

The repellent- impregnated jackets do have some problems. 
They are not very durable, especially when worn while walking or 

86 



hiking through wooded areas , often catching on branches and 
snagging or tearing. They also pose a risk around fires because 
of their flanunability. They should not be worn near open flames 
or while smoking. 

vi. Personal Hygiene 

Mosquitoes may be attracted to people by the carbon dioxide 
they exhale, their movement, the colour of their clothing, their 
body heat and their body odours. Although there is little 
scientific information available on this topic, persons who 
perspire heavily, work under strenuous conditions, and thereby 
generate significant body odour may be more susceptible to 
mosquito bites, other things being equal. Thus, good personal 
hygiene, coupled with the other protective measures, may reduce 
the number of mosquito bites that person would otherwise receive. 

For the same reason, people may wish to avoid the over-use 
of colognes and hair sprays, some of which may be attractive to 
mosquitoes . 

vii. Human Vaccination 

Fox (1982) assessed the use of vaccination to protect humans 
from WEE. Currently available only to a relatively few laboratory 
and field workers who are at greater risk, human vaccination, if 
feasible, would be a means of controlling outbreaks of 
encephalitis in endemic areas. Although some research has been 
carried out on human vaccines, none of the vaccines developed have 
proven to be sufficiently antigenic to produce long-term immunity. 

Because of the high research and development costs that 
would be involved, the risks and costs associated with large- 
scale vaccination programs, the instability of developmental 
vaccines and the infrequent occurrence of encephalitis outbreaks, 
it would appear that human vaccination for protection against 
mosquito -borne encephalitis currently is not a practical 
alternative. 

viii. Devices for Protection 

Many gadgets are marketed, from time to time, claiming to 
protect people from mosquito bites while they are outdoors. These 
include small, battery-operated mosquito repellers and backyard 
zappers . 

All of the electronic devices that have been subjected to 
scientific investigation have proven not to have any significant 
effect on the number of mosquito bites that a person will receive. 

ix. Horse Vaccination 

Horses are especially susceptible to mosquito bites because 
of the potential for prolonged exposure in the field. Many horses 
have, over the years, been bitten by mosquitoes carrying 
encephalitis virus. Some suffer nervous system disorders; others, 
death . 

Since the late 1930' s, a vaccine for protecting horses 
against WEE has been available. A vaccine has also been developed 

87 



that protects horses against both WEE and EEE in those areas where 
both diseases are endemic. 

Vaccination programs have led to a significant reduction in 
the number of horse cases of WEE in Manitoba over the past 15 
years. Theoretically, it is possible to protect all horses 
against these diseases (i.e., WEE, EEE) in Canada. However, 
because horses are dead-end hosts and, thus, play no role in the 
spread of these diseases to humans, vaccination of horses will not 
protect humans (Anonymous 1978) . 

Horse owners wishing to protect their stock should consult 
their veterinarian for advice on this matter. 

x. Repellents for Horses 

Many repellents are available for use on horses to protect 
them from mosquito bites (Appendix 1) . These repellents may be 
applied by spray or cloth pad. Their main drawbacks include their 
short duration of protection (usually less than 3 hours) , their 
cost and the time it takes to apply them to one or more large 
animals. Most veterinarians and farm supply stores carry a range 
of approved repellent formulations. 

xi. Smudges 

Smudges, are an old-fashioned, yet effective, method of 
repelling mosquitoes within a limited area. Common in rural areas 
and camp-sites (but usually not allowed by law in urban settings) , 
smudges have been used to protect people and livestock from the 
bites of mosquitoes and other biting flies. 

Smudges often are made by placing rotting wood, leaves or 
damp straw over a well-established fire to generate clouds of 
smoke. Horses quickly learn to stand downwind in the smoke to 
obtain relief from mosquito bites. 

xii. Insecticides 

There are several inseticides registered in Canada for 
protection of horses from mosquito attack. Because of local 
problems with availability of various insecticide formulations, 
persons interested in using these materials are advised to consult 
their regional agriculture extension representative. 



88 



7. EMERGENCY VECTOR CONTROL 

a. Emergency Vector Control by Municipalities 

As outlined above, in the section on vector suppression, 
emergency vector control (whether it be a large-scale 
provincially-operated program or a smaller- scale , municipally- 
operated program) is much more than simply deciding to spray, 
ordering some insecticide and hiring staff and equipment to treat 
the community(ies) at risk. The many elements of such an 
operation must be carefully considered before beginning an 
emergency spray program. In this section emergency mosquito 
vector control by municipalities, either alone or in conjunction 
with a provincially-operated vector control program is discussed 
in general terms . 

Most, if not all, emergency vector control programs carried 
out by municipalities will be done in conjunction with a 
provincial program. It would be difficult to conceive of a city 
or town attempting to initiate an emergency program without prior 
provincial approval, financial support or other involvement. Any 
municipal mosquito vector control program, whether routine or 
emergency, would require approval from provincial regulatory 
agencies. Further, it would be relatively easy for a province to 
stop a municipality from carrying out an emergency program with 
which it did not agree, simply by revoking their pesticide 
applicator licences and program permits. Thus, if an emergency 
situation developed in only one municipality, nothing of an 
emergency nature could be done without that municipality and the 
province agreeing on a course of action. 

The reverse would not necessarily hold. If a municipality 
did not wish to be included in a provincially-operated vector 
control program, it would have little power to stop the operation. 
Obviously, any political differences which might exist between the 
two governments would have to be put aside during a localized or 
regional mosquito -borne disease outbreak and they would have to 
cooperate fully with each other. 

Based on Manitoba's experience with WEE outbreaks, a 
municipality with an on- going mosquito control program would be in 
a good position to step-up its operations from routine to 
emergency vector control almost immediately. Following political 
approval of additional expenditures for the accelerated vector 
control program, the necessary extra personnel could be hired, 
materials could be purchased, and the program could be expanded. 
Such local efforts should be encouraged because they could offer a 
degree of protection to the public while the province was involved 
in organizing a larger- scale vector control program. 

Initially, the municipal vector control operations might be 
done independently but, once the provincial program started, the 2 
programs would have to be coordinated. 

If the municipality had the necessary resources, both 
mosquito larviciding and adulticiding could be carried out. Given 
the required trained staff, spray equipment and insecticides, 
mosquito larviciding could be carried out during the day and 

89 



mosquito adulticiding during the night. A municipality with 
limited resources might concentrate its larviciding efforts on 
treating known vector breeding sites (for Culex tarsalis , these 
sites would include discarded tires, barrels, and other 
containers, plus such temporary and semi -permanent aquatic 
habitats as ditches, sloughs and marshes) and its adulticiding 
efforts on applying residual sprays to areas adjacent to these 
breeding sites. 

On the other hand, a municipality with adequate resources 
might expand its normal larviciding zone around its built-up 
areas, reducing inward mosquito dispersal, and might adulticide 
all of its residential areas on a rotational basis, killing adult 
mosquito vectors already present throughout the city or town. 

The key elements of such municipal mosquito vector control 
programs are described below. 

Vector Control Methods , Materials and Equipment 

Most on- going mosquito abatement programs emphasize mosquito 
larviciding. Larvicides are applied to known mosquito breeding 
sites to destroy the immature mosquitoes before they become a 
nuisance or health hazard. Mosquito adulticiding, on the other 
hand, is usually considered a back-up measure, designed to reduce 
adult mosquito populations, if and when larviciding has been 
inadequate for some reason. 

In the case of new mosquito larviciding programs, most of 
the larval breeding sites are mapped out before spraying begins. 
Over the course of several years, abatement officials develop an 
inventory of such breeding sites, enabling more efficient 
larviciding operations to be carried out. A municipality that has 
had such a program for many years is in an excellent position to 
carry out an emergency larviciding program. 

Mosquito Adulticiding 

If a municipality does not know where the mosquito breeding 
sites are when a health emergency is perceived, it might be best 
advised to forego any attempt at larviciding, concentrating' all of 
its resources on mosquito adulticiding. The main target, in any 
case, would be the adult mosquito vector. Only the adult female 
mosquitoes may have the virus after they have become infected from 
their first blood- feeding and are then capable of transmitting the 
disease. The only way in which these infective mosquitoes can be 
destroyed efficiently is by a mosquito adulticiding operation. 

Mosquito adulticiding involves either the application of 
thermal or cold insecticide aerosols along street and lanes 
(thermal fogging and ultralow volume [ULV] spraying or cold 
fogging, respectively) or the application of residual sprays to 
mosquito resting areas. The adulticide may be applied by back- 
pack sprayers or by truck-, trailer-, or aircraft-mounted 
sprayers . 

Most municipalities with established mosquito control 
programs will have ground-based programs. Some may supplement 
their ground-based larviciding operations with aerial larviciding 

90 



(e.g. Winnipeg), mainly using helicopters. A very few may have 
the capacity to carry out both aerial larviciding and aerial 
adulticiding (e.g., Edmonton). Such well-equipped operations will 
be directed by experienced professionals who have acquired 
expertise over a period of years. Aerial adulticiding is 
described in other sections of this manual. The discussion below 
will be limited to describing ground-based, emergency, mosquito 
adulticiding programs which can be implemented fairly quickly, 
given the necessary resources. 

It should be emphasized that mosquito adulticiding will only 
reduce mosquito vector populations temporarily. Even if 95+% of 
the mosquitoes present are destroyed, the remaining mosquitoes 
still have the potential to transmit the virus. Over the course 
of several days, additional adult mosquitoes will add to this 
residual population, dispersing into a treated area from 
neighbouring untreated areas and emerging from larval breeding 
sites within the treated area. Thus, the public should not rely 
entirely on the municipality's efforts to control the mosquito 
vector. Although the vector population may be decimated by 
mosquito adulticiding operations, the public still should be 
encouraged to use personal protection to further reduce the risk 
of being bitten by any remaining infective mosquitoes. 

Fogging 

Generally, fogging is more effective, efficient, economical 
and practical than residual spraying. The "fog" (i.e. minute 
aerosol droplets) generated by the specialized sprayers that are 
used in mosquito fogging is carried about 100 m downwind through 
an infested area, killing resting and flying mosquitoes in its 
path. Residual sprays, on the other hand, must be applied 
directly to those areas where mosquitoes are expected to rest 
during daylight hours. 

Mosquito fogging may involve the use of either thermal or 
cold fogging equipment. Thermal foggers (both portable and 
vehicle -mounted) use an insecticide which has been mixed with an 
oil (e.g. diesel, fuel oil) prior to application. The 
insecticide -oil mixture is vaporized in a special heat chamber of 
the thermal fogger and, aided by an air blast, the resulting gas 
condenses when it comes into contact with cooler air, forming a 
dense cloud of fine droplets which drifts downwind, away from the 
fogger. 

Cold foggers do not use heat to form similar spray droplets. 
An air blast, coupled with a specially-designed nozzle, breaks the 
liquid insecticide concentrate into small droplets. Rather than 
forming a dense, white cloud like the thermal fogger, the cold 
fogger generates an inconspicuous mist. 

Cold foggers (e.g. Leco, MicroGen) are more technologically 
advanced than thermal foggers (e.g. Tifa, MicroGen). The droplets 
produced by cold foggers are of a very narrow size range, designed 
to be optimum in size for killing mosquitoes, and the insecticide 
flow rate is more precisely-controlled. The net effect is that 
they destroy more mosquitoes, use less insecticide, and do not 

91 



cost as much to operate. 

Other advantages include the fact that they present less of 
a traffic hazard than the dense white cloud produced by thermal 
f oggers . Also, because the insecticide is much less conspicuous, 
cold fogs do not bother those people who are opposed to fogging as 
much as thermal fogs do . 

The tiny droplets generated by such foggers are carried 
downwind through the area to be treated. The droplets, most of 
which are suspended on air currents drift through vegetation and 
around obstructions. They impact or impinge on rough surfaces, 
including mosquitoes. These droplets, whether they impinge or 
continue drifting downwind, evaporate over a period of hours. If 
they impinge on the hairs or scales of a mosquito, the insecticide 
penetrates into the mosquito, causing its death. Such 
insecticidal fogs are generally effective against mosquitoes for 
up to about 100 m. Beyond that distance, the droplets usually 
have become too small through evaporation and have dispersed too 
widely to impinge on and kill mosquitoes. 

There are many brands of thermal and cold foggers (see 
Appendix) available through such Canadian dealers as KemSan Inc. 
and Sanex Inc. Abatement officials directing large mosquito 
control programs in Canada can offer advice on the performance of 
the various brands available. Dealers should be contacted for 
detailed information on the models currently available. 
Consideration should be given to price, delivery time, staff 
training and the availability of parts and service. The most 
efficient foggers are large, heavy-duty units that are mounted in 
the back of pick-up trucks. Portable foggers may be useful in 
some situations (e.g., along woodland paths, between buildings) 
but they are relatively inefficient and labour-intensive. 

ULV equipment also can be mounted on aircraft. In a 
municipal situation, ULV nozzles (e.g., Beecomist nozzles) have 
been mounted on helicopters for treating large, recreational 
areas . This approach may be very useful when such areas cannot be 
treated using ground-based equipment where such equipment might 
damage wet turf or because the areas are heavily wooded or 
otherwise inaccessible. 

Many different mosquito adulticides are registered for use 
in ground-based equipment. The insecticides currently registered 
for this purpose are listed in one of the attached appendices. 
The choice of adulticide will depend on the spray equipment 
available, cost and relative human and environmental safety. To 
make an informed choice, one should obtain technical information 
on the product from the manufacturer (including specimen labels, 
material safety data sheets, technical bulletins, and unit 
prices) . As for spray equipment selection, other mosquito 
abatement officials may be the best source of information on the 
performance characteristics and problems associated with the 
various brands and models. 

One would expect thermal fogging and cold fogging to be 
equally effective in controlling Cx. Carsalis and other vector 
species provided that the insecticide is applied according to 

92 



label directions, the equipment is accurately calibrated and 
spraying takes place when mosquitoes are most active (i.e., peaks 
in activity occur 1 hour before and up to 3 hours after sunset and 
0.5 hours before and up to 2 hours after sunrise). It should be 
noted that, on some days, mosquitoes may be fairly active 
throughout the day because of warm, humid, cloudy, calm weather 
conditions. Also, fogging has a flushing action on mosquitoes, 
stirring even resting mosquitoes to flight, perhaps through a 
repellent action. However, these conditions cannot be depended 
upon. It is still best to concentrate the fogging efforts at 
sunset and sunrise for maximum effect on the mosquito vector 
population. 

A municipality can estimate its requirements for fogging 
equipment and adulticide by considering the number of km of 
streets, lanes and roads that can be fogged, the insecticide flow 
rate and the vehicle's operating speed. Assuming 6 hours of 
fogging per night, under optimum weather conditions (i.e. 
temperatures of 12-28° C, windspeeds less than 16 km/h, relative 
humidities of 35-95%), and knowing how often one wants to fog an 
area, one can calculate the number of fogging trucks and the 
amount of insecticide required. 

Given the opportunity to purchase new mosquito adulticiding 
equipment, serious consideration should be given to replacing old 
thermal f oggers with new ULV sprayers . The many advantages ULV 
sprayers have over thermal f oggers should not be ignored. 
Although they may be slightly more expensive to purchase than 
thermal f oggers, they will cost less to operate. 

Ideally, fogging trucks should drive perpendicular to the 
prevailing wind for even dispersal of the fog. This is usually 
not possible, especially in new suburban areas with numerous 
crescents and bays. Usually, the trucks must simply follow 
existing road systems, with unavoidable gaps and overlaps 
occurring. 

During routine mosquito adulticiding operations, it is wise 
to respect the wishes of those opposed to fogging, leaving their 
properties and an adequate buffer around them untreated. However, 
during an emergency adulticiding operation, local authorities may 
choose to treat all properties alike, advising any persons opposed 
to spraying to close their windows and stay indoors while spraying 
takes place. 

Residual Spraying 

Residual spraying can have an important role in vector 
control. Applied to the surfaces of vegetation on which 
mosquitoes rest, residual sprays usually remain toxic to 
mosquitoes for one to several days before being destroyed by 
sunlight, moisture, and / or high temperature. If fogging 
equipment is unavailable, residual spraying for adult mosquito 
control should be the next choice for adult mosquito vector 
control. 

Spraying plant surfaces (e.g. shrubs, tree trunks, tall 
grass, weedy areas [especially close to mosquito breeding sites]) 

93 



will destroy mosquitoes resting on these surfaces over several 
days. Only water-based emulsions should be used (especially on 
such high value plants as ornamental shrubs) because oil -based 
sprays frequently "burn" the foliage of sensitive plant species. 
Such plants are usually listed on the insecticide container label. 

Portable sprayers can be used effectively to apply a coarse 
spray to dense vegetation in backyards and along paths in parks, 
golf courses and other recreational areas at times when people are 
absent. Truck- or trailer -mounted sprayers are most efficient 
along accessible road, rail and transmission line rights -of way. 
Aircraft also have been used to apply residual sprays, usually 
along large, relatively inaccessible, drainage ditches with 
intermittent stagnant water. Environmentally- sensitive areas 
(e.g. bird sanctuaries, school grounds) are best omitted from such 
operations. 

Spraying should be done according to approved label 
directions. Optimum vector control will occur if residual 
spraying is done when temperatures are between 12-28° C, winds are 
low (i.e. less than 16 km/h) , and the risk of precipitation, while 
the residual spray dries on the plant surfaces, is minimal. 

Occupational Safety 

Because the personnel involved in insecticide handling, 
mixing and application will be exposed to insecticide for extended 
periods of time during the emergency vector control program, it is 
very important that these people be provided with and use all 
necessary protective clothing and gear. Specific requirements may 
vary with the worker's activities and the insecticide's toxicity. 
Occupational safety and health officials, the manufacturer and the 
container label will provide advice on what protective measures 
are necessary. 

Generally, applicators should wear protective coveralls, 
rubber boots , rubber gloves , goggles , and an approved agricultural 
respirator when exposed to spray mists. Persons mixing 
insecticides may also wear rubber aprons or rain suits for added 
protection from spills or splashes. These items usually are 
readily available from safety supply dealers in major cities. 

Also, good personal hygiene practices should be encouraged. 
Workers should clean their safety gear daily, replacing components 
as necessary. Clean clothes should be worn each day. Hands 
should be washed before eating or using the washroom. Showers 
should be taken before changing into clean clothes. Such 
precautions will minimize any possible chronic absorption of 
insecticide into their systems. 

Coordination of Control Operations 

As noted above, municipal and provincial vector control 
operations will rarely, if ever, run independent of each other. 
The operations must be coordinated for maximum effectiveness. 
Once the provincial program of aerial ULV application is scheduled 
for a city or town that has been carrying-out mosquito 
adulticiding while waiting for the provincial program to get or- 

94 



ganized, that municipality should cease adulticiding and switch 
over its staff and equipment resources to mosquito larviciding. 

This change in operations will avoid unnecessary overlaps in 
adulticiding efforts, further reduce the potential for virus 
transmission, avoid possible confusion over liability claims and 
reduce complaints from those opposed to spraying. 

One way in which provinces can encourage cooperation from 
such municipalities is to agree to pay all of the costs incurred 
by the municipality in its efforts to reduce local vector 
populations. Obviously, municipalities would be well-advised to 
carefully record all expenses they incur which are directly 
related to emergency vector control even if the work is done 
before the province agrees to pay all or a portion of the costs 
involved. 

b. Value of Ground-Based Control 

Ground-based adulticiding, using a ULV truck-mounted aerosol 
generator, is often initiated or increased when an emergency 
vector control program is considered necessary. Due to the large 
areas involved in outbreaks of WEE and the urgency with which the 
treatment must be conducted, ground- based adulticiding can only 
supplement a larger scale aerial operation. 

Weather conditions, vehicle speed, insecticide flow rate, 
and the optimum droplet size are specific for the equipment and 
the insecticides selected. Regarding droplet size, the objective 
is to obtain a narrow range of sizes so that 80 to 90% of the 
droplets are 5-20 u in diameter and have a volume median diameter 
(VMD) of 10u-17u (Mount et al . 1975a). 

Most bioassays to evaluate the effect of a given adulticide 
on mosquitoes, using ground-based aerosol generators, have been 
conducted using caged mosquitoes in open areas. Mosquitoes are 
placed at various heights above ground, at distances of 50 to 200m 
beyond and perpendicular to the path of the equipment (Mount et 
al. 1968; Mount et al. 1975a, b; Rathburn and Boike 1975; Rathburn 
et al. 1981; Walker and Meisch 1982). The results indicate high 
levels of mortality. However, the results using caged mosquitoes 
placed in wooded or protected sites indicate low to medium 
mortality (Taylor and Schoof 1971; Womeldorf et al. 1973). 

Caged mosquitoes placed under shrubs or trees during aerial 
treatments of ULV propoxur and ULV malathion were also protected 
from the insecticide droplets, resulting in reduced mortality 
(Brust 1984; Brust and Ellis 1976b; Ellis and Brust 1982). 

Only a few studies have evaluated the effect of ground- 
based aerosol treatments on natural populations of gravid Culex 
mosquitoes in urban areas. Results vary from no reduction of egg 
rafts laid by gravid females of Cx. pipiens complex and Cx. 
restuans, to 50X reduction for 1 to 4 days following treatment 
with ULV malathion (Leiser et al. 1982; Strickman 1979). The size 

95 



of the treatment area, the dispersal rate of gravid females, the 
sample size and the environmental conditions at the time of 
treatment can affect the level of control. It is therefore 
important to replicate the experiments on different nights and to 
treat areas large enough to be representative of an operational 
program. This appears to have been done in a long term study on 
the effect of ULV ground-based adulticiding conducted by Geerey et 
al. (1983). An analysis of 32 area-wide treatments over 5 years 
in a Chicago suburb showed that Culex females were reduced by 27% 
for 3 nights following the malathion treatments. The reduction 
during the first night was 392 and on the second and third nights , 
24 % and 18% respectively. 

Natural populations of mosquitoes may escape most of the 
aerosol treatment due to the protection afforded by tall grassy 
vegetation, trees, shrubs, hedges, fences, houses and other 
buildings. When caged Culex spp. were placed 10m from a 
residential street, mosquitoes were readily killed by a ULV 
application of malathion. However, when cages were placed 115 m 
from the street, in vegetation along alleys, the mosquitoes 
survived. The mean mortality in caged mosquitoes placed at 
various distances from the truck-mounted aerosol generator in the 
urban area of South Bend, IN was 26% (Leiser et al. 1982). 

Insecticide droplets must make direct contact with 
mosquitoes if the application is going to be effective in killing 
adults. The best results would be expected when mosquitoes are in 
flight. Mosquito flight activity decreases sharply during the 
darkest part of the night (Nelson and Spadoni 1972) , and 
adulticiding may be less effective during these hours. 

In Winnipeg, Manitoba, during 1977 to 1984, where an average 
of an estimated 150 sq. mi. were treated with ULV ground-based 
adulticiding equipment in 7 nights (Ellis, pers. comm. ) the 
reduction in trap counts of Cx. tarsalis has been calculated to be 
68% following a treatment (Raddatz 1985) . This reduction was not 
based on experimental results of mosquito mortality following 
adulticiding, but was calculated rather as a factor in the trap 
count model that gave the best estimate of parameters that 
explained the variables in the trap counts during 7 summer seasons 
in Winnipeg. Because a minimum of 7 nights were needed, and 
because of unsuitable weather conditions, it usually required more 
nights to treat the Winnipeg area. There was no way to estimate 
the % control on different nights after treatment. The estimate of 
68% control appears high compared to that shown for the Chicago 
area by Geery et al. 1983). 

c. Assessment of Repellents 

The alternatives that are available to protect people 
against mosquito -borne encephalitis include direct mosquito 
control using insecticides and/or host protection by means of 

96 



personal protection, vaccination, screening, behaviourial 
modification, suitable clothing, and sanitation. The term, 
"personal protection" , is defined here as the use of an approved 
insect repellent by a person to prevent mosquito bites. Following 
an introduction to the insect repellents registered in Canada for 
protection against mosquitoes, the safety and effectiveness of 
DEET, the active ingredient common to most repellents, will be 
reviewed. 

DEET is an effective repellent against more than 20 genera 
of insects and related arthropods. A wealth of scientific 
literature has been published on DEET on the chemistry, 
toxicology, and effectiveness of DEET over the past 36 years. 
Those interested in an in-depth review of DEET may wish to consult 
the bibliography prepared by Rut ledge et al. (1978) and the DEET 
pesticide registration standard prepared by the U.S. EPA (Panetta 
et al. 1980). The latter document is a comprehensive review of 
the toxicology and efficacy of DEET. 

Repellents must provide a 2+ hour protection time before 
they can be registered for use in Canada. Several different 
active ingredients, alone or in combination, are used in repellent 
formulations. Repellents are registered with Agriculture Canada 
to protect against ticks, black flies, biting midges, horse flies, 
deer flies and mosquitoes. The per cent active ingredient(s) 
present in a formulation of repellent may vary considerably from 
product to product. Domestic class insect repellents can be 
purchased in a variety of forms including liquids, pressurized 
aerosols, sticks, foams, towellettes or wipes and impregnated 
fabrics. Given the large number and variety of repellents that 
are available to consumers for direct application to their skin, 
their safety and effectiveness need to be re -assessed on a regular 
basis to ensure that they meet current standards. 

It is beyond the scope of this section to review the safety 
and effectiveness of every active ingredient used in mosquito 
repellents. However, DEET, alone or in combination with one or 
more of the other active ingredients, is the primary ingredient 
most commonly found in repellents. Thus, this assessment will be 
limited to DEET as a single active ingredient in a repellent 
product. It is not intended to be an exhaustive review. Rather, 
it attempts to address those concerns raised by public health 
officials over the widespread use of repellents during an 
encephalitis outbreak. 

Toxicology of DEET 

DEET has been marketed in Canada for over 30 years. In the 
U.S.A., an estimated 50-100 million people use a repellent each 
year. Most repellents sold contain DEET as the sole or primary 
active ingredient. Extrapolating from these U.S. estimates, 5-10 
million people probably use a repellent each year in Canada. 

97 



There have been numerous anecdotal reports of skin 
irritation following applicationof repellents, several cases of 
toxic systemic reactions from repeated use of products containing 
DEET (mostly children; most recovering but some ending in death) 
and several deaths following ingestion of products containing DEET 
(MMWR 1989). 

Adverse effects are always attributed to DEET, even though 
the products involved may have been a mixture of DEET and several 
other active ingredients. The safety record of repellents is 
excellent considering the numbers of persons using them annually 
to obtain relief from the annoyance and bites of insects and ticks 
and to protect against arthropod-borne disease. On the other 
hand, any adverse effects, even in a very small segment of the 
human population, should underline the need for carefully 
conducted toxicological and epidemiological studies on all of the 
active ingredients used in repellents and the need for precautions 
to be followed explicitly in their use. 

Dermally- applied DEET is rapidly absorbed through the skin 
and excreted in the urine of laboratory animals. Thus, bio- 
accumulation is expected to be minimal. DEET is excreted 
secondarily via the feces, lacrimal glands and the nasal mucosa. 

Rates of excretion in urine varies with the species 
(Blomquist and Thorsell 1977): 

o 80% excretion in 24 hours in guinea pigs; 
o 90% excretion in 8-40 hours in mice; and 
o 68% excretion in 24 hours in rats. 

Studies of human metabolism of DEET are not very complete. 
Although up to 49% of dermally- applied DEET is lost through 
evaporation (Spencer et al. 1979), excretion rates are variable 
among the few individuals studied. For example, when 52 mg of 
DEET was applied to the forearms of 4 human volunteers, 13.3% was 
recovered in the urine in 24 hours , 15.3% by 48 hours and 16 . 7% by 
12 days (Feldman and Maibach 1970) . Using 1 volunteer Blomquist 
and Thorsell (1977) showed that, when 2 applications of 0.12 mg/kg 
body weight was applied to the forearm, 5.5% was recovered in the 
urine in 48 hours after the first application and 3.8% was 
recovered in 48 hours after the second application. In a third 
study (Markina and Yatsenko, 1971), 20-40% DEET creme formulations 
were applied to 15 volunteers. No toxicity was reported after 30 
days of daily application. Most of the DEET absorbed through the 
skin (>96%) is excreted in the urine within 24 hours. 

A small percentage of individuals exhibit skin irritation 
and allergic effects from use of 15-100% DEET formulations. Skin 
irritations, rashes, hives and blisters as well as eye, nose and 
mouth irritations have been reported (Hollebone pers. comm.). 

98 



Repeated applications of DEET may cause drying and 
irritation of the skin, especially around the nose area (Ambrose 
et al. 1959; Phillips et al. 1972). There are reports of 
illnesses, including nausea and dizziness, after repeated 
applications of DEET. Neurological events associated with the 
repeated use of DEET have been observed. In 1989, 5 reports of 
generalized seizures, occurring 8-24 hours after DEET use, were 
investigated in New York and Connecticut where DEET use has 
increased due to the concern over Lyme disease (MMWR 1989). Four 
cases were 3-7 year-old boys; one was a 29 year-old man. All 
recovered. It is not known whether or not their illnesses were 
directly attributable to DEET use. 

Some trans -placental effects may occur in pregnant small 
animals, but the reproductive effects, if any, in humans are 
unknown. DEET may decrease implantations but does not appear to 
be a spermatogenetic agent. 

Although the general toxicity of DEET is low, it appears 
that the data available on DEET (and other active ingredients of 
repellents) and human toxicology are not adequate to assess 
clearly the chronic or sub-chronic effects of repeated doses of 
DEET. The U.S. EPA has identified a number of data gaps (Panetta 
1980) . Exposure studies to determine the effects of repeated use 
of DEET formulations should be initiated. 

Several precautions should accompany any promotion of 
repellents as a means of personal protection during an outbreak of 
mosquito-borne encephalitis. The following list of precautions is 
based on one given in a recent MMWR (1989) : 

o Apply repellent only to exposed skin or clothing. 

o Avoid applying high-concentration products to the skin, 
especially children. 

o Avoid inhaling and ingesting repellents and getting into 
the eyes . 

o Wear long sleeves and long pants to minimize the skin 
area that must be treated. 

o Avoid applying repellents to children's hands which are 
likely to contact their eyes or mouths. 

o Never apply repellents to irritated skin or wounds. 

o Use sparingly; one application will usually last 2-8 
hours . 



99 



o Wash repellent off the skin after coming indoors, 
o If an adverse reaction occurs, wash treated skin and call 
a physician; take the repellent to the physician. 

The effectiveness of a given insect repellent may be 
affected by a number of inter-related factors including weather 
(ambient temperature, wind, humidity, etc.), mosquito biting 
pressure, mosquito species, user physiological characteristics and 
state (i.e., subject susceptibility), formulation ingredients and 
characteristics (absorption rate, evaporation rate, etc.), loss 
through abrasion, and application rate. Given all the possible 
combinations of factors, it is understandable that different 
products give different levels and periods of protection, 
depending upon the unique conditions occurring when they are 
evaluated. This variability is reflected in the technical and 
scientific literature (Panetta et al. 1980). 

DEET loss, through abrasion, evaporation or washing off the 
skin or through absorption into the user's body, will result in 
reduced effectiveness. Increased wind velocity, increased 
temperature, rain and sweat can decrease efficacy by 50-90% (Khan 
et al. 1973; Gilbert et al. 1957; Goulk et al., 1971; Schieffer et 
al. 1976). Cutaneous absorption of DEET also may reduce efficacy 
(Mailbach et al. 1974). 

The minimum effective dose on human skin required to repel 
caged Aedes aegypti appears to be 0.02-0.2 mg DEET/cm 



8. ENVIRONMENTAL MONITORING 

a. Spray Dispersal 

Whenever pesticides are sprayed, especially from aircraft, 
some material inevitably drifts outside the target zone. The 
amount of material lost from the target zone depends on the 
application technology, weather, topography, and the pesticide 
formulation. Different spray techniques deliver different ranges 
of droplet sizes, with ultra- low- volume equipment typically 
delivering droplets with a mass median diameter in the 70-100 um 
range (Randall 1977) . The size of spray droplets is an important 
factor in determining the distance they drift, with droplets 
larger than 100 um drifting very little unless the wind during 
application is very strong. However, after emission from the 
nozzle droplets begin to evaporate, and they decrease in size. 

The theoretical development of relationships between droplet 
diameter and fall time has been given by Seymour (1969) , who 
illustrated the time for a droplet of given initial size to be 
reduced to zero. For example, a 100-um droplet of water would 
last only about 6 seconds at 30 % relative humidity (RH) , about 11 
seconds at 50 X RH, and about 12 sec at 70 % RH. Smaller droplets 
and the vapour produced from them move both horizontally and 
vertically with air motion, and may drift off the target zone, 
sometimes for quite long distances , leaving the target zone to 
recieve less than the ideal amount of material which was emitted 
from the sprayer. For example, Armstrong (1977) reported that 4 
to 100 X of Orthene emitted by a spray aircraft was deposited on 
spray blocks. When propoxur was applied by aircraft to Winnipeg 
in 1975 and 1981, generally less than 20 % of the pesticide 
emitted from the aircraft could be accounted for by measurements 
of deposits (Manitoba Clean Environment Commission, 1982) . 
Ware et al . (1984) monitored deposits of fenvalerate applied 
aerially to cotton and found that off -target deposits declined 
quickly with distance from the target zone out to about 100 m, and 
then less strikingly out to at least 400 m downwind, where they 
were still 1-10 X of those in the target zone. The actual 
distance the drifting material can travel has no practical limit 
if the material is stable to decomposition. It may be carried 
long distances with air mass movements either in the gas phase or 
adsorbed to suspended particles. For example, DDT from forest 
spraying in New Brunswick and Maine was thought to have been the 
source of DDT detected in rainwater in the Magdalen Islands 
(Pearce et al. 1978). Sheehan et al . (1987) have summarized the 
topic of off-target drift (their chapter 5), and Table 1 is 
abstracted from their summary. 

Within the target zone, the surface to volume relationship 
of receiving areas will determine to a large extent the 
concentration of pesticide received. Aerial sprays are generally 

101 



applied to deliver the desired amount to a two-dimensional surface 
within the spray zone, but the pesticide is actually dispersed in 
three dimensions. For example, in the instance of a body of water, 
the simplest case is one in which the water is mixed throughout 
and so the greater the volume per area of sprayed surface, the 
greater the opportunity for dilution. In such a simple case, a 
large shallow pool would experience a higher concentration than a 
small deep pool with the same volume. The surface film itself 
provides a concentrating mechanism for movements of the pesticide 
either from air to water or from water to air, and organisms using 
the surface habitat are particularly prone to exposure. 

Once deposited pesticides re-volatilize from surfaces such 
as soils or foliage at rates that depend on the temperature, wind, 
vapour pressure of the pesticide, the formulation, and the nature 
of the surface (Wheatley, 1973). The pesticides may then be 
dispersed further throughout the environment. For example, 
several pesticides including chlorpyrifos and malathion have been 
reported recently in fog droplets at concentrations much higher 
than those expected on the basis of Henry's Law constants 
(Glotfelty et al. 1987), and so these pesticides can be dispersed 
with fog droplets. 

While the phenomenon of off- target drift has been documented 
many times, the concentration of pesticide reaching non- target 
zones is clearly subject to the mathematics of dilution, and 
exposure of animals or plants outside the target zone will almost 
always be much less than exposure within the target zone. Other 
modes of application would be expected to generate less off- 
target drift than aerial application. 

b. Effects on Wildlife 

The effects on wildlife are of two general kinds. Firstly 
there are the direct toxicological effects due to exposure to the 
pesticide being applied, and secondly there are the indirect or 
secondary effects of changes in one species on the biology of 
another (Hurlbert 1975) . With regard to the direct toxicological 
effects, the critical parameters are exposure and toxicology. 

Exposure is related to the amount of chemical an organism 
takes in per unit of time, and the duration over which the intake 
occurs. Toxicology is related to the chemical and physical 
properties of the pesticide and to the means by which exposure 
takes place (dietary, contact, inhalation, etc.). Discussion of 
the effects of a pesticide needs to start with the environmental 
chemistry of the pesticide since that will determine the exposure. 
However, this subject has a very large literature and will be 
treated only superficially here. 

Most pesticides used for mosquito control in North America 
are designed to remain active for only short periods after 
application. A list of pesticides registered for mosquito control 

102 



in Canada is given in Appendix I, and application rates range up 
to 550 g ai/ha. An example of rapid 'disappearance' of three 
organophosphorus insecticides (temephos, Reldan, and 
chlorpyriphos) from the water column of small polyethylene -lined 
pools was given by Hughes et al . (1980), who found that over 90% 
of all three compounds frequently 'disappeared' in less than 2 
days. The polyethylene apparently acted as a sorbent for the 
compounds, particularly chlorpyrifos , to first remove it from the 
water, and then gradually to supply it back and contribute to a 
residual effect. MacKenzie et al. (1983) followed the loss of 
temephos from mosquito breeding ponds in Ontario and found that 
residues in the water declined over 24 hr, but that residues in 
bottom sediment increased over that period and then declined over 
the following several days. Residues derived from temephos were 
still present in at the end of the sampling period, particularly 
in sediments, but they consisted principally of sulfoxide and 
sulfone metabolites rather than the parent pesticide. 

Rapid disappearance can be explained by an array of processes 
which act to remove or change the pesticide after it is emitted, 
including photolysis, hydrolysis, adsorption, volatilization, and 
metabolism by different organisms. In water hydrolysis is often 
important in destroying the parent compound (and in creating new 
products) , and the rate of hydrolysis is often described as a 
'first-order' process in which the amount hydrolyzed at any 
instant depends on the amount of parent compound present at that 
time. This gives rise to an exponential decline in the amount 
remaining, often described by the half- life of the compound. For 
example, Marshall and Roberts (1978) summarized studies on the 
hydrolysis of chlorpyrifos, and cited earlier work showing the 
dependency on pH and temperature, as shown in Table 2. At constant 
pH, hydrolysis was much faster at higher temperature, and at 
constant temperature, hydrolysis was much faster at more alkaline 
PH. 

The most widely used measure relating exposure and direct 
toxic effects is the exposure that is acutely lethal under defined 
test conditions. With terrestrial animals this is usually the 
single dose given orally that results in the death of half the 
treated animals over some arbitrary but defined observation 
period. With aquatic animals, the "dose" is usually expressed as 
the concentration supplied in the water rather than the amount 
actually taken into the animal. 

Chemical pesticides generally have little or no specificity 
for the target pests; if specificity is achieved it is through the 
application which attempts to maximize exposure of the pest 
without at the same time unduely exposing non- target species. 
Where the habitat of target and non- target species overlaps, 
however, applications will reach both. The acute toxicities of a 
few common pesticides to Culex mosquitoes, along with toxicities 

103 



to non- target midges are presented in Table 3 (abstracted from 
Sheehan et al . , 1987). The acute toxicities are similar for both 
groups, and is clear that these pesticides do not discriminate 
between the mosquitoes and the midges. 

Some additional data on toxicity of common pesticides to 
other non- target invertebrate fauna are listed in Table 4, from 
Mayer and Ellersieck (1986). 

In contrast to the conventional pesticides, some of the newer 
insect growth regulators appear to be selectively more toxic to 
target pests than to non- target fauna. Table 5 (abstracted from 
Brown 1978) is a list of the toxicity of methoprene and 
diflubenzuron to mosquito larvae and to several non- target taxa. 
Methoprene in particular is much more toxic to the mosquito larvae 
than to the other invertebrates tested. 

The safety of fish and wildlife is perhaps of greater 
immediate concern to more people than that of invertebrates . Some 
concentrations acutely lethal to rainbow trout are given in the 
Table 6 below and oral doses toxic to laboratory rats are given in 
Table 7. 

The more subtle effects of pesticide exposure on non- target 
animals are obviously much more difficult to demonstrate, 
particularly in natural populations. However concepts and 
methodologies are beginning to emerge to detect signs of stress in 
ecosystems (Levin et al. 1983; Rapport et al. 1985). Some of the 
clearest cases have been with older organochlorine compounds (see 
review by Ripper 1956), but these will not be discussed here 
because they are no longer in use for arbovirus vector control in 
Canada. There are also convincing cases with organophosphours 
insecticides, and some of these are discussed below. 

Organophosphorus and carbamate insecticides act on synaptic 
transmission by inhibiting acetylcholinesterase enzyme activity, 
and a number of cases of enzyme inhibition in non- target organisms 
has been recorded. For example, Lockhart et al. (1985) reported 
inhibition of about 75 X of the brain acetyl cholinesterase 
activity in young fish stocked in shallow ponds sprayed with 
malathion for control of mosquitoes. The fish in this case (no 
predators) were apparently not harmed permanently because they 
survived. Their enzyme activities recovered to near pre -treatment 
levels in about two weeks , and the only evidence of ecological 
harm was a temporary cessation in growth. 

Some more subtle effects of cholinesterase inhibitors have 
been noted in higher integrative functions. For example, exposure 
of young Atlantic salmon to fenitrothion increased their 
vulnerability to predation by brook trout (Hatfield and Anderson 
1972). In rats, reduction of brain cholinesterase activity to 40- 
60 X of normal resulted in increased numbers of mistakes in 
solving problems presented by a maze (Banks and Russell 1967) . 
Treatment of f idler crabs Uca pugnax with temephos resulted in 

104 



impairment of their ability to escape predation by birds (Ward et 
al. 1976). 

There have been reports of bird kills after applications of 
organophosphorus insecticides and brain cholinesterase activities 
have been used as an aid in diagnosis. Diazinon applied to a golf 
course was implicated in the death of a small number of Canada 
geese in Missouri (Zinkl et al. 1978). Brain cholinesterase 
activities were about one third of those from control birds with a 
comparable brain storage history. 

At the population level one of the most convincing examples 
of effects of insecticide applications acting on a species other 
than the target species has been the proliferation of prey after 
removal of predators. Killing non- target zooplankton has 
frequently produced an upsurge in algal numbers due to decreased 
cropping (Hurlbert 1975) , and this has been reported following 
applications of insecticides for mosquito control in Canada 
(Hughes et al. 1980) . 

Perhaps the best -documented effect of pesticide spraying has 
been the development of pest populations resistant to the 
pesticides. In a recent review of this problem, worldwide there 
are now 447 species of insects and mites resistant to at least one 
insecticide (Georghiou 1986) . The order of insects with the 
greatest propensity to develop resistance, unfortunately, includes 
the common vectors of viral infections, namely the Diptera, with 
156 resistant species. Furthermore, of these 156 species of 
resistant Diptera, 132 are of medical or veterinary importance, 
while 23 are of agricultural importance. Many of these species are 
resistant to several classes of insecticides, with the current 
accounting as shown in the Table 8. 

c. Effects on Humans 

The effects of pesticide applications are of three general 
types: benefits to human health and economic prosperity inherent 
in the control of disease vectors; direct toxicological effects on 
people exposed to the pesticides; indirect effects on people 
through changes in ecosystems. 

Perhaps the clearest case of the benefits of vector control 
to people is DDT in tropical regions. Metcalf (1973) concluded 
that DDT campaigns eradicated malaria in 37 countries with a 
population of 728 million people, and gave partial or complete 
control in 80 more countries with 618 million people. In India, 
for example, cases of malaria declined from 100 million annually 
in 1933-35 to 150,000 in 1966, and deaths fell from 750,000 per 
year to 1,500. 

It is not uncommon for pesticides used for biting fly control 
to reach people through pathways independent of uses against 
biting flies. Gartrell et al. (1986) tabulated the quantities of 
pesticide residues found in typical U.S. food items as shown in 

105 



Table 9. Obviously people consuming common food items are 
experiencing ongoing low levels of dietary exposure to a range of 
pesticides including some used for biting fly control. Given 
multiple exposure pathways leading to people, it seems unlikely 
that effects of pesticides used for biting fly control will be 
separable from effects of the same pesticides used for other 
puropses, except in the instance of acute effects associated with 
known local applications. 

For obvious reasons most information on the direct 
toxicological effects of pesticides on people comes from 
accidental exposures, occupational exposures of people who work 
with pesticides, and occasionally suicides or homicides. However, 
there have been a number of experiments with human volunteers , 
many of which have been listed by Hayes (1975). For example, Laws 
et al. (1967) gave oral doses of temephos to volunteers (prison 
inmates in Puerto Rico) at up to 256 mg/man/day for 5 days, or 64 
mg/man/day for 4 weeks with no clinical symptoms or side effects 
noted, and no effect on red blood cell or plasma cholinesterase 
activities. Similar experiments with methoxychlor given orally to 
human volunteers (prison inmates in Alabama) were reported by 
Fabian et al. (1971). Methoxychlor given at rates up to 200 times 
the levels permitted by the U.S. Food and Drug Administration had 
none of the effects expected on the basis of prior experiments 
with rats. Exposed rat experienced changes in fatty acid 
distribution, inhibition of spermatogenesis, and alterations in 
the ultras true ture of intestine and liver, and these effects were 
sought but not found in the people . 

Survey data on people who work with pesticides have not 
revealed unusual incidences of diseases, as compared with the 
population not exposed to pesticides occupationally, however, 
pesticide workers did suffer an unusually high frequency of death 
by trauma (Morgan et al. 1980). During the 1960s, medical students 
at the University of Montreal interviewed members of farm families 
where pesticides were used on apple orchards. About one third 
(520 out of 1661 interviewed) complained of symptoms (mainly eye 
irritation, fatigue, and headache) for a short period (up to 7 
days) after spraying (Jegier 1969). Malathion has been shown to 
induce contact sensitization in some people (Milby and Epstein 
1964). 

It has been argued that substantially over 10,000 people are 
killed annually worldwide by exposure to pesticides, generally 
through exposure during application (Loevinsohn 1987) , but little 
of this would be expected to be associated with biting fly control 
in North America. 

Recently published Federal guidelines for the water quality 
do not give permissable quantities for any of the pesticides used 
commonly for mosquito control (Canadian Water Quality Guidelines 
1987). 

106 



One effect which should not be underestimated is the fear 
people express when exposure to pesticides seems unavoidable. 
This is analagous to fear of exposure to radiation, and it is 
noteworthy that a U.S. court considering the re -opening of the 
Three Mile Island nuclear plant ruled that the Nuclear Regulatory 
Commission must concern itself with popular fears about the 
reactor, regardless of whether or not the fears have a rational 
basis (Marshall 1982) . People often associate high risk with the 
uses of pesticides. The risks associated with 30 different 
activities or technologies were ranked by four different groups of 
people, and pesticides ranged from 4th to 15th. 'Experts' ranked 
pesticides 8th behind motor vehicles, smoking, alcohol, handguns, 
surgery, motorcycles, and x-rays (Slovic 1987). 

Indirect effects on people through pesticide actions are much 
more difficult to document, except for the economic or public 
health effects for which the application was made. The common 
examples include contamination of fish and wildlife leading to 
intake by people with possible biological effects on the people 
(Jacobson and Jacobson 1988) but these examples generally refer to 
stable halogenated compounds. However, the methodologies emerging 
to deal with older compounds may also offer promise of detecting 
subtle effects of less stable pesticides used for biting fly 
control. Also of concern to people are effects of pesticides on 
non- target species of interest to humans for aesthetic or economic 
reasons, as discussed earlier. 



107 



Table 1. Off- target deposits of aerially applied 
pesticides. Deposit as per cent of application rate. 



Pesticide 


50 m 
downwind 


100 m 
downwind 


500 m 
downwind 


malathion 


6.5 


1.5 


0.04 


azinphos methyl 


10.5 


0.9 


0.2 


methoxychlor 


1.2 

1.1 


0.9 
0.9 


0.09 
0.1 


fenvalerate 


- 


0.5 


0.15 



Abbreviated from Table 5.3 of Sheehan et al . 1987 



108 



Table 2. Rate of hydrolysis of chlorpyrifos in phosphate buffered 
(0.02 M) distilled water at 15 C to 35 C, and an initial 
concentration of 0.12 mg/L. 



Temperature 


pH 


half-life 


duration of experiment 


deg. 


C 




( days ) 


(days) 


15 




8.1 


53.5 


29 


25 




8.1 


22.9 


28 


35 




8.1 


4.5 


12 


15 




6.9 


99.6 


29 


25 




6.9 


35.2 


28 


35 




6.9 


11.5 


26 


15 




4.7 


206.3 


29 


25 




4.7 


62.8 


28 


35 




4.7 


15.9 


28 



From Marshall and Roberts (1978), Table 2.2. 



109 



Table 3. Comparative toxicities of chemical pesticides to 
mosquitoes and other non- target aquatic invertebrates. 

24-hr LC 50 (ug/L) 



Insecticide 



mosquitoes 
Culex spp 



midges 



chlorpyrifos 
malathion 
methoxychlor 
del tame thr in 
carbaryl 



0.3 
3.4 
8.9 
0.02 
75 



1.2 

68.0 

18.9 

0.23 

418 



0.5 - 7.0 
7.0 - 100. 
1.6 (96 h) 
0.02 - 0.29 
10 (48 h) 



From Sheehan et al . 1987 



110 



Table 4. Acute (96-hr) toxicity of several pesticides to non- 
target aquatic invertebrates.* 

96 -hr LC 50 (ug/L) to 



malathion 

chlorpyrifos 

propoxur 

temephos 

methoxychlor 



Gammarus 
lacustris 


Pteronarcys 
californica 


-- 


10 


0.11 


10 


34 


18 


80 


10 


.80 


1.4 



Mayer, F.L. , Jr., and M.R. Ellersieck (1986) 



111 



Table 5. Acute toxicity of methoprene and diflubenzuron to aquatic 
invertebrates . * 



Species 



24-hr LC 50 (ug/L) 



diflubenzuron 



methoprene 



Mosquito (Aedes) 
Clam shrimp (Eulimnadia) 
Tadpole shrimp (Triops) 
Cladoceran (Daphnia) 
Mayfly nymph (CallibaeCis) 
Dragonfly nymph (Orthemis) 
Midge (Chironomus) 
Backswimmer (Notonecta) 
Protozoan (Paramoecium) 
Amphipod (Hyalella) 
Water boatman (Corisella) 
Beetle larva (Hydrophilus) 
Copepod (Cyclops) 
Seed shrimp (Cypicercus) 



0.5 


0.008 


0.15 


1000 


0.8 


5000 


1.5 


900 


50 


-- 


50 


20000 


10 


10 


10 


1200 


-- 


1250 


-- 


1250 


-- 


1650 


100 


50000 


200 


4600 


500 


1500 



From Brown (1978) p. 150 



112 



Table 6. Concentrations of several pesticides acutely lethal to 
rainbow trout in 96 -hour exposures.* 



Pesticide 


Fish wei 


-ght 


Temperature 


LC 50 




(g) 




(C) 


(ug/L) 


malathion 


1.4 




12 


200 


chlorpyrifos 


1.4 




13 


7.1 


propoxur 


1.2 




13 


8200 


temephos 


1.3 




12 


3490 


methoprene 


0.6 




12 


1600 


methoxychlor 


1.2 




12 


62 


diflubenzuror 


i 1.0 




10 


>100 



Data from Johnson and Finlay (1980) 



113 



Table 7. Acute oral toxicity of several pesticides to laboratory 
rats. 



Pesticide 



Toxicity 
(Oral LD 50 ) 



Reference 



malathion 
chlorpyrifos 

propoxur 

temephos 
methoxychlor 



1375 mg/kg 
82-245 mg/kg 

80-191 mg/kg 

ca 1000 mg/kg 
5800-7000 mg/kg 



Hayes (1975) 

Marshall & 
Roberts (1978) 

National 
Research 
Council (1982) 

Cyanamid (1970) 

Gardner & 
Bailey(1975) 



114 



Table 8. Numbers of species of Diptera resistant to several 
classes of insecticides. 



Number of species Class of insecticide 
of Diptera insects resist 



108 DDT 

107 Cyclodienes 

62 Organophosphorous 

11 . Carbamates 

10 Pyrethroids 

Fumigants 

1 Other 

Retabulated from Georghiou (1986) 



115 



Table 9. Daily intake of selected pesticides calculated from residues 
in typical U.S. foods. 



Pesticide Average daily intake (ug/day) 

carbaryl 0.825 

chlorpyrifos 0.241 

malathion 16.8 

methoxychlor 0.249 



116 



9. PUBLIC INFORMATION 

a. Information Program 
Objectives 

The objective of the emergency public information program is to 
provide complete, current and factual information to the target 
audiences on all aspects of the encephalitis outbreak. Given timely and 
accurate information, the media and the public may more readily support 
government actions. The following areas require special attention. 

Information on the Disease 

The disease, whether it is St. Louis Encephalitis (SLE) or Western 
Equine Encephalitis (WEE) or some other mosquito -borne encephalitis, 
must be described in terms understandable and specific to the target 
audience. For example, medical doctors will require information on the 
diagnosis and treatment of encephalitis whereas mothers with young 
infants will require information on recognizing the symptoms of the 
disease in babies. Other audiences, such as the news media, may wish a 
historical perspective on the disease. 

In addition, the general public will require a basic overview of 
the disease, including such aspects as what the disease is, how it 
affects people, the typical symptoms of the disease, how the disease is 
transmitted, how the level of risk is monitored, what people can do to 
minimize the risk to themselves and members of their family, what 
measures can be taken to reduce transmission of the disease, and so on. 

Information on Vector Control Measures 

Any large-scale disease control program undertaken by the 
government will generate considerable media attention, especially on a 
regional basis. The news media and their audiences will want to know, 
in as much detail as possible, what measures are being taken to minimize 
the risk of disease transmission. They will want to know who is 
directing the control operations, what specific operations are involved 
in emergency mosquito control, and what are the pros and cons of the 
insecticide that is being used to control the vector mosquitoes. 

Control Officials 

People want to know who is directing the emergency mosquito control 
program. "Control Officials" is a collective term which includes the 
persons directing the control operations, from a policy point-of -view 
(i.e. elected officials) and from a technical point-of -view (i.e. field 
operations personnel).. The ultimate decision makers (including the 
decision to initiate control measures and what scale of operation) are 
the elected officials, including the Minister of Health and the Minister 
responsible for emergency measures. Other members of Cabinet may be 
involved in the approval of funding, waivers of Acts and Regulations, 
defending government actions, etc. The key decision maker is the 
Minister of Health and that person will be the focus of public and media 

117 



attention. 

The person(s) directing the emergency mosquito control operations 
in the field should be technically-qualified to oversee the operations 
base (usually at the airport), recommend applicators, insecticide, 
insecticide suppliers, etc. They should be experienced in mosquito 
abatement, knowing when conditions are optimum for mosquito control. 
They should be able to liaise with elected officials (particularly the 
Minister of Health), senior administrators, suppliers and staff at the 
operations base. Ideally, the person directing the program will have 
successfully supervised similar, large-scale mosquito control operations 
in the past and have the confidence of the public. 

This person's decisions will have considerable impact on the 
success of the disease control program. Although some media exposure 
will be necessary, it should be kept to a minimum to allow this person 
to carry out the work without the added pressure of dealing with a 
sometimes aggressive and adversarial media. 



Application Method 

The public will want to know that the government is taking all 
reasonable steps necessary to minimize the health risks associated with 
the disease as quickly as possible. The media will want to know that 
the disease control operations are done using the most suitable methods 
and materials available. The most efficient and economical means of 
wide-area mosquito vector control is the aerial application of 
insecticide . 

The spray operations should be done by experienced aerial 
applicators, using large, multi-engine aircraft. Large aircraft (e.g. 
DC-6) can carry sufficient insecticide to treat a small city during one 
flight. Two- or, preferably, 4 -engine aircraft also provide that extra 
margin of safety necessary for low- level flights over developed urban 
and rural centres . 

The optimum method of adult mosquito control is the application of 
very small droplets of insecticide over the area to be protected. In 
theory, these tiny droplets slowly drift through the area where 
mosquitoes are flying or resting. A few droplets, impinging on the body 
of the mosquito, are enough to kill the mosquito. Such ultralow volume 
applications (abbreviated ULV) require relatively little insecticide per 
unit area to be effective. 

However, many factors may reduce the overall effectiveness of the 
ULV application. Control will never be 100%. Changing wind conditions 
during the period of aerial application may cause the ULV droplets to be 
unevenly dispersed over the control zone. Heavy vegetation (e.g. thick 
bush, tall, dense grass) and dense concentrations of buildings and 
fences may filter out many of the droplets and provide cover for some of 
the mosquitoes. In some cases, monitoring of mosquito mortality may 
indicate that re -treatment is necessary. 



118 



Insecticide Used 

Inevitably, the government will have to defend, first, the large- 
scale use of insecticide and, second, the specific insecticide chosen 
for use. Depending upon the number of confirmed human cases of 
encephalitis at the time, the defence may be relatively simple or 
complex. Foremost in minds of all the target audiences will be the 
question, "Is this insecticide safe?". 

This general question will have a multitude of facets. Is it safe 
to breathe? Will it cause cancer? Should I keep the kids indoors? 
Will it ruin my garden vegetables? Will it hurt my flowers? Is it safe 
to pets? Will it mar my (very expensive) car finish? Should we cancel 
the baseball game? Can we still have our outdoor wedding party? Will 
it kill the butterflies? Will it kill my bees? These and dozens of 
other questions centre on the question of the safety of the insecticide 
to human health and environmental acceptability. 

Obviously, these questions will be asked by the public and an 
information package on this topic should be prepared beforehand to 
answer at least the most commonly -asked questions. Much of this 
information is available from the insecticide manufacturers and can 
readily be obtained from them and from other sources such as the federal 
departments of Agriculture and Health and Welfare. 

The key point here is cost-benefit. In simple terms, are the 
potentially harmful effects of the insecticide more or less desirable 
than the potentially harmful effects of the disease? On one side of the 
equation, the monetary costs associated with spraying can be tallied 
(including the costs of the insecticide, the insecticide application, 
and any damage associated with the application [e.g. bee kill]). On the 
other side, one can estimate the number and ages of persons who might 
contract the disease and the costs associated with their health care and 
lost earning potential. Unfortunately, many of the costs and benefits, 
on both sides of the equation, are either intangible or speculative and, 
thus, their defence is open to criticism. Nevertheless, knowing, for 
example, that $1 million worth of dead bees is equivalent to the life- 
long, health care costs associated with one infant who becomes paralysed 
or mentally retarded from the disease may provide some perspective. 

Information on Personal Protection 

Practical advice on personal protection from mosquito bites, to 
people living in regions where mosquito -borne encephalitis is possible, 
should be provided whenever there is a potential disease outbreak as 
determined by vector/virus surveillance. Personal protection is simply 
taking precautionary steps to minimize being bitten by mosquitoes. 
These range from adjusting personal schedules or activities to avoid 
peak periods of mosquito activity or areas of high mosquito abundance, 
to covering exposed skin with clothing and wearing mosquito repellents . 
Minimizing the number of mosquito bites minimizes the risk of virus 
transmission from the infective mosquito to people. 

119 



Repellents containing N, N-Diethyl meta- toluamide (DEET) are 
effective against mosquitoes. There are numerous formulations 
available, allowing for personal preferences. Repellents that contain 
Dimethyl phthalate are also effective against mosquitoes, and are often 
preferred for personal (less oily; DEET disolves hard plastic objects) 
or health (allergy) reasons. Repellent- impregnated, mesh clothing is 
available for persons who do not wish to wear repellent directly on 
their skin. Infants, who should not be treated with repellents, may be 
kept indoors or protected with mosquito netting when they are outdoors . 

The public should be advised to wear repellents when they are 
exposed to mosquitoes as soon as an impending disease outbreak is 
perceived and throughout the period of risk. They should be advised to 
change their activities and schedules, where possible, to avoid the dawn 
and dusk periods when mosquitoes are generally most active, particularly 
in those areas where mosquitoes are very abundant. Persons who are 
occupationally most at risk (e.g. farmers) or most at risk because of 
their age (e.g. infants, the elderly) should take special precautions to 
avoid bites. 

b. Media Option 

Information can be provided to the public through the news media 
and through paid and/or unpaid public service announcements. Usually, a 
combination of approaches is taken because the news media tends to 
develop sensational feature stories on victims of the disease and the 
vector control operations rather than to issue simple, precautionary 
advice from health officials on such things as using mosquito 
repellents . 

Public Service Announcements 

During past health emergencies, such announcements have been 
published at government expense in daily newspapers to ensure that the 
public is given concise, accurate information on the disease and its 
control. Caught up in the popular issues of chemical safety, 
environmental concerns, etc., the news media may not be interested in or 
understand the importance of providing such basic information to the 
public. 

Faced with this possibility, public information officers should 
prepare a series of such announcements in advance so that they can be 
issued quickly when the need arises. 

Press Releases 

Press releases contain the information that the issuer wishes the 
news media to pass on to the public, hopefully unchanged. But, to the 
news media, such releases are only possible story ideas which may be 
worth investigating further through personal interviews. Rarely, if 
ever, are press releases passed on to the public unaltered. Often, the 
stories take bizarre twists and turns leaving the issuer wishing that 
the press release had never been issued. 

120 



Nevertheless, press releases are a tradition that continues. One 
can only attempt to make the most of the situation by anticipating where 
the press release may lead the reporter and being ready to deal with 
each direction the reporter may take. This means having the factual 
information and/or information sources available to respond to reporters 
questions. Ideally, the information sources will be consistent and 
confirm any information that has been provided in the press release. 
However, the more people that are involved, the greater the chance that 
some of these people will contradict each other, even professionals who 
are supposedly working towards the same goal. 

News Conferences 

News conferences are often the forum of choice for persons issuing 
information to the public through the news media. Typically, the news 
conference is held in a room which has been set-up to facilitate, 
physically, the work of the both the issuer and the reporters. The 
format is simple. Someone, usually a public information officer or 
administrative assistant, introduces the speaker and says a statement 
will be issued, after which the speaker will respond to the reporter's 
questions. A written copy of the statement is usually issued at the 
same time . 

The speaker gives his statement and the reporters ask their 
questions. Sometimes, statements will be delivered by the person in 
charge but he answers only questions of a general or policy nature, 
deferring responses to questions of a technical nature to selected 
experts (e.g. a health official, an entomologist, a veterinarian) 
sharing the stage. Other times, there may be a series of government 
speakers and statements issued, each speaker fielding questions on their 
area of expertise after delivering a statement or all of the statements. 



c. Resource Materials 

Reference material is essential during a health emergency, 
particularly during an outbreak of mosquito-borne encephalitis. 
Information on relevant topics should be available for the public 
information program. Much of the needed information is contained in the 
various sections of this Manual and additional material may be obtained 
from experts in the various fields if gaps are perceived or more detail 
is required on specific topics. 

Health officials of many different jurisdictions, after 
experiencing a mosquito or other arthropod-borne disease outbreak, have 
seen the merit in preparing audio -visual materials to describe the 
disease, the vectors and disease prevention and control. A modern 
classic example is the wealth of such materials prepared on tick-borne 
Lyme disease. Further, they have seen the merit of preserving every 
scrap of information they can obtain that documents an encephalitis 
outbreak, their unofficial information collections records rivalling any 
archival record. Such resource materials range from informative notes 

121 



to comprehensive film documentaries. 

Persons involved in the public information program would be well- 
advised to find out who was involved during past health emergencies. 
Who was the epidemiologist, entomologist, veterinarian, medical doctor, 
archivist, freelance writer, environmentalist? etc. Equally important, 
one should know if those key players were for or against past emergency 
measures, if only to develop a list of resource persons. 

The resource materials, whether they be scientific publications, 
technical manuals, program reports, posters, videos, public service 
announcements, or any other form of documentation, can be grouped under 
the following headings. 

Diseases 

Resource information on SLE and WEE should include historical 
accounts of past outbreaks; descriptions of the viruses and the symptoms 
of disease in humans; the distribution and incidence of the diseases in 
Canada and other jurisdictions; the prevalence of viral antibodies in 
the general population; the age groups and occupational types most at 
risk; fatality rates; the seasonal history of the diseases; clinical 
features; diagnosis; and the known and speculative parts of the 
transmission cycles. 

Vectors 

Information on the vectors of SLE and WEE should include 
descriptions of their life cycles; geographical distribution and 
seasonal abundance; larval breeding sites; blood-feeding requirements 
and sources of blood; blood- source seeking behaviour; flight activity 
periods; dispersal range; day-time resting sites; effect of weather on 
vector activity, abundance and virus transmission; methods and materials 
used to monitor larval and adult vector populations. 

Control Methods 

Reference material under this topic might be grouped under such 
headings as vaccination of horses; mosquito larviciding methods, 
materials, and equipment; mosquito adulticiding methods, materials and 
equipment; reduction of larval mosquito breeding sites; biological 
control of mosquitoes. 

Insecticides 

Information on the mosquito larvicides and adulticides which may be 
used for disease vector control can be assembled quickly if requested 
from the right people. For each insecticide involved, technical 
information might be grouped under such headings as toxicology, 
environmental impact; use restrictions; precautions; mode of action 
against mosquitoes; efficacy; residual activity; emergency procedures 
and contacts; suppliers; unit costs. 

Personal Protection 

122 



Useful information on personal protection might be grouped under 
such headings as repellents; repellent- impregnated clothing; protective 
clothing; screened doors and windows; avoidance of mosquito bites. Each 
of these headings, in turn, might have a series of sub-headings. 

For example, under repellents, information could be grouped on the 
relative effectiveness of the various repellents available; how mosquito 
repellents work; the pros and cons of wearing mosquito repellents; who 
should and who should not wear repellents; local sources, stocks and 
costs of repellents. 

Posters 

A series of posters, depicting symptoms of the disease, the 
transmission cycle, horse vaccination, the mosquito life cycle, and 
methods of mosquito control, would be useful for display in doctors' or 
veterinarians' offices, schools, and selected public buildings. Such a 
series of posters was developed after a recent outbreak of WEE in 
Manitoba. 

Videos 

A documentary videotape on dealing with a outbreak of encephalitis 
would also be useful. The media would be able to select portions for 
incorporation into news reports, saving them time and effort in 
obtaining difficult to obtain footage. By itself, it might be excellent 
teaching material for public education in schools. Again, such a video 
was prepared for Manitoba Health after a recent outbreak and copies may 
be available. 

Films 

Films have been prepared on encephalitis control in the U.S.A. 
However, these films may not be applicable to Canadian conditions and 
are now out-of-date, in terms of the insecticides available and the 
equipment used in mosquito control. 

Advertisements 

Paid, public service announcements were part of the 1981 WEE 
outbreak in Manitoba. Copies of these should be available in provincial 
archives . 

Media/Public/Private Archives 

Whenever the news media develops a major news item, it reviews its 
historical records for archival reference and resource material. Such 
reviews quickly allow a reporter to formulate an overview of the issues, 
develop a list of experts (often adversaries) to contact for information 
and outline possible approaches to the story assignment. Old 
documentary photographs and video-tapes are a source for new, supporting 
visual elements of the story. 

Persons responsible for the government's public information program 
also would find such material very helpful in assembling a comprehensive 

123 



public information package. It would certainly be worthwhile to review 
copies of any such material that might be on file from previous health 
emergencies. Knowing what the media knows, soon will know, or soon will 
want to know enables their questions to be answered with confidence, 
consistency and accuracy. Also, knowing what visual features the news 
media will likely want to update (e.g. mosquito biting victim, veter- 
inarian vaccinating a horse, sick horses, Government Cabinet meeting in 
progress, spray planes being loaded, spraying in progress) often enables 
these requests to be anticipated and arranged at convenient times rather 
than endured while surveillance and control officials are under greater 
pressure . 

d. Specific Needs 

Each target audience has special information needs. Some examples 
are given below. 

Chemically- sensitive persons 

Such individuals will want more detailed information on the 
insecticides used and repellents recommended and on the schedule of 
spray operations over their community. They will also want to know what 
they can do to minimize their exposure to the insecticide. 

Doctors 

Medical doctors may require more detailed information on the 
symptoms and diagnosis of the disease, the procedures to follow for 
proces'sing blood samples, and the treatment that should be followed. 

Mothers with infants 

Special advice should be provided to expectant mothers and mothers 
with infants. Such topics include personal protection without 
repellents and what symptoms of the disease in infants will require 
attention. 

Horse Owners 

A horse owner, whether caring for the family pet or a thorough- 
bred racer, will want to know what has to be done to protect the' horse 
from mosquito bites and the disease. 

Beekeepers 

Beekeepers will want to know the exact boundaries of spray blocks, 
the times of spray applications, what measures they can take to protect 
their bees from exposure to the insecticide sprayed, and what they may 
have to do to support any claims for bee kill or lost honey production 
they may make. 

Farmers 

Farm families, outside sprayed areas, will need special attention, 
emphasizing personal protection from mosquito bites and source reduction 

124 



on their farm property. 
Veterinarians 

Veterinarians will need information on the disease in horses, 
timing of vaccinations, processing blood samples, and reporting and 
treating suspected horse cases. 

Elected Officials 

Elected officials, particularly mayors and reeves, will need to 
know what the risks of disease are to their specific communities and 
what, if any, plans, are being made to include their municipalities in 
any emergency spray program. The timely supply of information is 
critical for their support of the program at a local level. 



125 



PART II 



126 



1. SURVEILLANCE PROGRAM 

a. Protocols for Arbovirus Surveillance 

A Model: Western Equine Encephalitis 

Protocols for western equine encephalitis surveillance are 
presented as a model for arbovirus surveillance. These protocols 
are the absolute minimum essential to provide an indication of 
risk. Additional surveillance procedures ( see SURVEILLANCE, 4d) 
which re -enforce and expand the annual database for assessment of 
risk and provide a mechanism for improving the database are 
recommended WEE surveillance program developed in Manitoba remains 
the most detailed system of surveillance carried out in Canada. 

Co-ordination of Program 

The program should be supervised by a designated Co- 
ordinator, who is Chair of the Surveillance Committee, and who is 
responsible for reporting to senior administration in the 
Ministry/Department of Health. The Chair should also be given the 
responsibility of coordinating the funding authorized for 
arbovirus surveillance. 

The Committee is responsible for carrying out the 
surveillance program, and should, through the Chair, report to and 
be accountable to the Ministry/Department of Health. The terms of 
reference of the surveillance committee should be well-defined and 
restricted to an advisory role. 

b. Resource Requirements for Surveillance Program 
Stable Funding 

Staffing 
co-ordinator 

permanent staff of program (areas of expertise must include 
virology, public health (infectious diseases, epidemiology), 
medical entomology, veterinary health (horses, poultry), 
meteorology, administration), 
seasonal staff 
office staff 
expert consultants (depending on expertise of permanent staff) 

Equipment 

laboratory facilities for virological work, laboratory facilities 
for mosquito handling, veterinary facilities for equine diagnosis 
and equine and chicken autopsies, vehicles for serum collection 
(including at least 1 truck), flock cages, mosquito traps, 
microscopes, cold tables, temperature recorders, rain gauges, wind 
recorders, chickens. 

127 



Supplies 

virological supplies, mice, reagents, picnic coolers (1+ per trap 
site), dry ice; entomological supplies, collection apparatus 
(aspirators), forceps, mosquito cages, cryovials, sealing tape, 
labels, repellent; sentinel flock supplies, repair kit, chicken 
feed (complete grower ration), medication, and water supply, 
capillary tubes; veterinary supplies, for collecting horse serum 
samples, autopsy samples; office supplies, including report 
preparation and distribution; travel support for field workers. 

c. Components of Surveillance Program 
i . Weather 

Weather data should be monitored over several points across 
the province, and interpreted by a meteorologist. Atmospheric 
Services of Environment Canada provide these services on a user- 
fee basis. 

Pre-season Assessment 

The following conditions should be reviewed and the 
implications on the current season assessed: soil saturation 
levels and late season rainfall of previous year, snowfall, mean 
average weekly temperatures for winter months , late winter/early 
spring mean average weekly temperatures , and anticipated rate of 
snowmelt. 

Seasonal Monitoring 

Weekly weather forecasts and updates should be prepared as 
data available on soil saturation levels. Retrospective weather 
reports on previous week should be prepared. 

Reporting Techniques 

Retrospective and forecast reports on conditions should be 
presented in a standardised format including weather map(s) 
covering surveillance area, and indicating weather stations/data 
collection sites. A narrative summary of weather conditions 
should be provided in a consistent weekly format, and be easily 
interpreted by people without scientific training or experience. 

ii. Mosquito Monitoring 

Flock traps : A detailed description of the flock trap is 
given by Wong et al. (1976), Wong and Neufeld (1982). Prior to 
each spring, all traps should be checked, and repaired as 
necessary. Flock trap cages are subject to vandalism as well as 
damage by animals attracted to the birds. Careful attention 
should be made to mesh screening, and attachment of mosquito 
trapping component. To protect traps from exposure to the 
elements, repaint, as necessary. Each trap/trap site should be 

128 



equipped with continuous max/min temperature recorders, rain 
gauges , wind recorders . 

Traps sites should be carefully selected, using the following 
criteria: site not too exposed but with reasonable vegetation 
providing shelter, proximity to breeding sites and preferred blood 
sources, history of surveillance or monitoring of mosquito 
populations, proximity to human population centres, safety from 
vandalsim, ease of access for surveillance crew, ease of 
maintenance (i.e., watering and feeding flock). 

Trapping Frequency 

Daily whenever possible; minimum of weekly (unless 
populations increases above non-outbreak levels) and biweekly 
during critical periods (mid June to mid July) . Mosquitoes should 
be sorted into five groups: Cx. tarsal is , Cx. restuans , Cs . 
inornaCa, Ae. vexans , and 'others' and counted (see 3 below). 

A minimum of five traps , located in different areas over 
jurisdiction; 12 to 15 traps are recommended. No additional traps 
should be set up in an emergency unless in areas where there is 
prior knowledge of WEE activity. 

Reporting Techniques 

Trap catches should be reported weekly and in a consistent 
format which includes three parts. 

1) tabulation for each trap site per trap/night (per trap/week for 
summaries): the total number of female mosquitoes caught, total 
number of Cx. tarsalis caught, and percentage of Cx. tarsalis of 
total number caught. 

2) graphic comparison both with average catch for non-outbreak 
years and average catch for outbreak years for the same collection 
period. 

3) a narrative presentation of trap results, interpreting counts 
to ambient conditions of temperature, precipitation, wind, and any 
other pertinent information (e.g., change to local environment). 
The narrative should also follow a consistent format, and be 
easily interpreted by people without scientific training or 
experience. 

Other trapping, including live trapping of mosquitoes for 
viral analysis with C0 2 -baited traps, and using standard New 
Jersey style light traps (see SURVEILLANCE 4b), is recommended. 
However, these trapping strategies are considered lower priority 
than a network of flock traps. 



129 



iii. Virus Activity 
Mosquito Isolations 

Mosquitoes should be collected daily from each flock trap by 
using a battery-operated aspirator. Mosquitoes removed from traps 
should be confined in mesh cages and transported, in coolers, 
promptly to the laboratory for immediate sorting and counting. 
Mosquitoes should be kept cool until and during counting. 
Mosquitoes should be retained on a cold table (-5 C) while being 
sorted, identified, and counted. Those mosquitoes retained for 
virological testing should be pooled according to species, trap 
location, and date of collection. Mosquitoes should be pooled and 
tested in the following priority: all Cx. tarsalis , all Cx. 
restuans , all Cs . inornata, and Ae. vexans for the remaining 
quota of weekly pools. Pooled mosquitoes should be live when 
processed, or kept frozen at temperatures -70 C until processing, 
to prevent loss of virus. (Where -70C storage is not immediately 
available, short term storage of pooled mosquitoes, well protected 
from exposure to carbon dioxide, at -40C in dry ice may be used, 
but only with risk of underestimating virus infection of 
mosquitoes. ) 

The number of pools processed weekly will vary according to 
trap catches , and may require the use of a weekly maximum number 
(quota) which depends on availability of resources. The number of 
pools to be processed should be consistent, annually. Pools 
should consist of a maximum of 50 mosquitoes per pool; and fewer 
for pools of Culex species, to allow more precise assessment of 
minimum field infection rates . 

Pools should be processed using recognized virological 
techniques. Several techniques are available, and the system 
adopted may depend in part on available expertise and facilities . 
Processing should be made and results confirmed within four to 
five days of pools being submitted for analysis (five to six days 
post collection) . Analysis by cytopathology in tissue cultures 
(embryo mice, or VERO, BHK-21, primary AFGMK cell cultures), with 
virus isolations confirmed by neutralization test (Sekla and 
Stackiw, 1976, 1982) is recommended. Identity of isolations 
should be confirmed by the National Arbovirus Reference Centre in 
Toronto. 

Reporting techniques- results of tests should be reported 
weekly and in a consistent format which includes three parts: 

1) tabulation of pools per date submitted, per species, per 
location, and including i) percentage (of total pools) of positive 
Cx. tarsalis pools/date/location, ii) percentage (of all Cx. 
tarsalis pools) of positive Cx. tarsalis pools/date/location, and 
iii) numbers of mosquitoes/pool. 

2) graphic comparison of season results to date with average 
results of non- outbreak years and with average results of outbreak 
years . 

130 



3) a narrative interpreting results and comparing results with 
frequency and extent of positive pools in average non- outbreak 
years as well as average outbreak conditions should also be 
provided in a consistent format. 

Sentinel Flocks 

Flock animals should be selected for survival under field 
conditions and handling. In Manitoba, the preferred sentinel host 
is a cross between Rhode Island Red and White broiler chickens 
(raised indoors), five weeks old at the beginning of surveillance. 
Flocks, consisting of fifteen birds each, should be set up, 
retained in flock trap cages (Wong et al. 1976, Wong and Neufeld 
1982) . Birds should be provided with a constant supply of fresh 
water, food and medication (Wong and Neufeld 1982). 

Birds should be tagged individually for identification. They 
should be established as free from prior exposure by a preexposure 
bleeding. Subsequent bleedings should be made biweekly unless 
indicators suggest above normal (i.e., above non outbreak) 
conditions, at which time birds should be bled weekly. All birds 
should be bled from the deep ulna vein, and the blood allowed to 
clot. Positive birds should be replaced with pre-bled birds 
(acquired at the same time as the sentinel birds, and maintained 
as potential replacement birds, as needed), calculations of rates 
of seroconversion should exclude replacement birds until they have 
been exposed for two weeks . 

Serological samples should be processed using recognized 
virological techniques. Haemaggluttination- inhibition (HI) and 
confirmation of HI positive samples with complement fixation (CF) 
(Sekla and Stackiw 1976, 1982) is recommended. An HI titre of 
1:32 should be considered evidence of seroconversion. Positive 
samples should be confirmed by the Animal Diseases Research 
Institute (Agriculture Canada), in Ottawa. 

Reporting techniques- results of tests should be reported 
weekly and in a consistent format which includes three parts: 

1) tabulation of rates of seroconversion per date and per 
location, including number of birds infected/site, number of birds 
surviving per site, and number of replacement birds placed per 
site. 

2) graphic comparison of season results to date with average 
results of non-outbreak years and with average results of outbreak 
years . 

3) a narrative interpreting results and comparing results with 
frequency and extent of seroconversion rates in average non- 
outbreak years as well as average outbreak conditions should also 
be provided in a consistent format. Interpretation of 
serconversion data should be made with account of mosquito 
monitoring data, virus isolation rates, and bird mortality. 

131 



iv. Equine Cases 

An inventory of veterinarians should be compiled and updated 
annually. Advisories should be sent out to all practising 
veterinarians informing them of the surveillance program, 
describing pattern of equine infections and listing symptoms of 
infection. In conjunction with the advisory, veterinarians should 
be requested to submit two blood samples from horses suspected of 
being infected to the provincial veterinary laboratory. The first 
sample (acute sample) should be taken at onset of symptoms; and 
the second, needed for confirmation of diagnosis, after two to 
four weeks. Sample submissions should include data on age and 
vaccination history of sick animals, and data on residency or 
travel in the area of possible infection. Veterinarians should 
also report frequency of horse vaccinations in their practice. 

Confirmation of equine infection should be carried out by HI 
test, with positives (of acute and subsequent samples) confirmed 
by complement fixation (CF) test, or neutralization tests for 
virus isolation (Sekla and Stackiw 1976, 1982; Wong and Neufeld 
1982). 

Confirmation of a diagnosis of WEE infection in horses is 
required, and should be based on the following criteria: 
i) paired samples (acute+subsequent) must show a 4 fold or greater 
increase in antibody titre (by HI or CF tests). 

ii) single samples (if no second sample is available) must show an 
HI titre of 1:64 in young (less than one year) animals with no 
history of vaccination and with CNS symptoms; an antibody titre of 
1:256 in horses of any age and immunization status; an antibody 
titre of 1:1024 in older horses with a known history of 
vaccinations . 

iii) Infection of horses which died without blood samples being 
collected can be confirmed by examination of brain tissue for 
lesions (if tests show animal is negative for rabies infection), 
or by presence of WEE virus confirmed by neutralization test. 

Positive samples should be confirmed by the Animal Diseases 
Research Institute (Agriculture Canada), in Ottawa. 

Reporting Techniques 

Incidence of possible equine infections and results of tests 
should be reported weekly and in a consistent format which 
includes three parts: 

1) tabulation of numbers of submission of samples of suspected 
infections/week, of numbers of confirmed cases submitted(by week 
of submission) /week, numbers of deaths/week. 

2) graphic comparison of season results to date with average 
results of non-outbreak years and with average results of outbreak 
years . 

3) a narrative interpreting results and comparing results with 

132 



frequency of suspected and confirmed cases in average non- outbreak 
years as well as average outbreak conditions should also be 
provided in a consistent format. Interpretation should include 
information on location and age of horse cases, status of 
suspected cases, and an account of exposure period, weather, 
mosquito monitoring data, virus isolation rates, and bird 
mortality. 

v. Human Cases 

Monitoring of human infections should not be part of 
predictive function of surveillance program, but should be carried 
out as part of the assessment of severity of an outbreak. 

Tests for WEE infection in patients are carried out at 
request of a physician. Blood sera should be analyzed by 
recognized techniques, which include HI and CF tests for 
screening, neutralization tests, and, if infection is recent, 
immunoglobulin M (IgM) antibody determinations (Sekla and Stackiw 
1982). 

Reports of suspect and confirmed cases should be reported 
immediately, with details of date of onset of symptoms, age, 
activity, residence/location of (suspected) infection. 

vi. Contributions and Activities from Other Jurisdictions 

Contributions from other jurisdictions are only useful if 
there is a formal agreement to contribute and if procedures , 
scheduling, and techniques are compatible with the surveillance 
program. Regular weekly contact with a supervisory personnel in 
other jurisdictions should be made by co-ordinator of the program. 

Weekly contact should also provide information on activities 
of other jurisdictions in mosquito control or in other insect 
control which may impact on surveillance data. 

Collaboration with Neighbouring Jurisdictions 

Information from neighbouring jurisdictions provides valuable 
information for the surveillance committee by assisting assessment 
of likelihood of virus activity. 

Reporting Techniques 

The co-ordinator should make regular, weekly (or less, as 
risk assessment requires) contact with supervisory contact person 
on a pre-arranged schedule. Exchange of information should be made 
in a consistent format. 

d . Approach 

Surveillance should be started early in the spring, and 
continue until fall. Staff should be hired, rather than volunteer 
help used, because of the requirement for reliability of regular 
trap collection which is not met when volunteers are used. 

133 



Account must be made of weekends, holidays, staff time off for 
field staff. 

A system of communicating information to the Minister of 
Health, the media, and the public must be planned well in advance. 
This should be coordinated through the Chair, and regular 
reporting times should be scheduled, and rigidly followed. 

Activity Schedule 

Setting up program: January -February 

Review areas of activity, procedures, lines of authority. 

Review criteria of risk; review objectives, annual 
procedures ; evaluate any innovations to program 

Arrange hiring of seasonal help 

Contact neighbouring jurisdictions; plan group workshop/joint 
meeting 

Schedule meetings on weekly basis 

Establish system of communications 

Make inventory of equipment, supplies 

March - April 
Train seasonal help 

Purchase equipment and supplies; repairs equipment as 
necessary 

April 

Prepare flocks and set up flock traps 

Prepare recording procedures, record sheets, maps of trap 
locations, record logs 

Arrange computer programming for report preparation 

Weekly Program 

Regular weekly update of surveillance status. 

Monthly program 

Plan reporting schedule 

Season wrap-up 

Prepare annual/seasonal reports and distribute. 



134 



2. CONTINGENCY PLANNING FOR IMPLEMENTATION OF 
EMERGENCY VECTOR CONTROL 

This section is a description of the general approach to 
aerial ULV applications, resource requirements, planning proce- 
dures, jurisdictions, operating procedures and reporting 
activities involved in emergency vector control during an outbreak 
of mosquito -borne encephalitis. Although the guidelines contained 
in this section are based on Manitoba's experience in dealing with 
outbreaks of Western Equine Encephalitis (in 1975, 1977, 1981 and 
1983), the basic concepts should be applicable to the control of 
other mosquito -borne diseases in Canada. As policies and 
procedures change over time and vary from province to province, 
changes should be expected. 

The technical information and advice given in this section 
are designed to assist someone who has been appointed to organize 
and direct an emergency spray operation, enabling a fast and 
organized response to the health emergency. In addition, it 
should help those officials and personnel who are supporting the 
field operation to understand what is involved in major emergency 
vector control. 

Although this section is designed to be a detachable field 
reference, users should refer to the first part of this manual for 
a review of the more general aspects of vector suppression, in 
both an emergency and a non- emergency context. 

a. General Approach to Aerial ULV Applications 

If the situation warrants, the Minister of Health will 
declare a health emergency due to the threat of mosquito -borne 
encephalitis. This decision will set the emergency vector control 
program into motion. Before the decision is made, an assessment 
of the risk to human health and the province's capacity to 
minimize that risk will have been made. Included in that assess- 
ment will have been a determination of the best way to reduce the 
mosquito vector population and, thereby, the risk to public 
health. 

Both ground-based and aerial vector control measures will 
have been reviewed. Aerial ultralow volume (ULV) application of 
insecticide will have been recommended as the most economical and 
efficient means of large-area mosquito vector control. The aerial 
application firm with the experience and equipment to apply the 
mosquito adulticide will have been contacted to determine its 
availability and how soon it can position itself within the 
province. The discussion below will assume that an experienced 
aerial application firm (such as Conair Aviation with a DC6 spray 
plane equipped with a Beecomist ULV spray system) will be hired. 
The supplier of the chosen insecticide also will have been con- 
tacted to determine how soon it can deliver the estimated 
insecticide requirements. Prices of these goods and services will 

135 



have been discussed if not negotiated and finalized. Arrangements 
will have been tentatively made to secure the required support 
personnel, facilities, equipment and cooperation that will be 
required during the health emergency. 

Coincident with these preparations, someone with the required 
knowledge and experience will be selected to direct the large- 
area mosquito vector control program. That person will likely be 
an entomologist who has managed a large mosquito abatement 
program, is familiar with the methods, materials and equipment 
used in major aerial ULV aerial applications of insecticide for 
mosquito control, and can draw on a network of professional 
contacts for advice and assistance as required during the course 
of the emergency operations . 

In preparation for the vector control program, the director 
of spray operations will be affirmed and, with the emergency 
measures coordinator, review what resources are required to carry 
out the vector control program in the safest, most economical and 
most efficient way possible. He will assist the emergency 
measures coordinator in setting up the field operations base at 
the nearest suitable airport and begin developing detailed spray 
block designs and a spray schedule with the aerial applicator. 

Once the field operations base has been established and the 
required support personnel, supplies and equipment have arrived, 
the operations director will oversee the actual spray operations. 
Progress at every step will be reported to and general direction 
will be received from the Deputy Minister of Health, through 
established channels. 

After the spray operations have been completed, the 
operations director will assist with the dismantling of the 
operations base, including such things as the return of unused 
insecticide to the manufacturer and the disposal of contaminated 
materials. He may also be involved in debriefing the Minister on 
the aerial spray program, in a review of the emergency expenses, 
and in the preparation of a report on the work carried out, 
including recommendations for future such programs. 

All of this may seem fairly simple and straight -forward. 
However, the description given above is only an outline of some of 
the key aspects of the vector control program from the operations 
director's point-of-view. Much more is involved. Plans for, 
organization of and operation of the aerial ULV applications is 
described in more detail below. Again, it is written from the 
perspective of the spray operations director. 

b. Resource Requirements 
Funding 

Emergency funding to cover all aspects of the health 
emergency (including surveillance, public information, vector 
control, efficacy evaluation, and environmental monitoring) will 

136 



be needed. Because the legislature will likely be in summer 
recess when the outbreak occurs, Cabinet will have to meet and 
approve the estimate expenditures. 

Cost estimates for the vector control operations will have to 
be developed, based on the number and sizes of the spray blocks, 
the insecticide required for their treatment, the cost of aerial 
application and various equipment and supplies needed. The 
Director of Spray Operations will assist in the preparation of 
these estimates. These estimates will be considered, along with 
those of the various supporting programs, by Cabinet. 

Operations Personnel 

The Director of Spray Operations, reporting directly to the 
Deputy Minister of Health, initiates and carries out the required 
activities of spraying cities and towns at risk. He coordinates 
all of the activities at the Field Operations Base to ensure that 
aerial spraying is carried out safely, efficiently and in a 
professional manner. He liaises with provincial and federal 
officials, university researchers and other organizations that 
monitor and assess the efficacy and impact of spraying. 

The person selected to be Director of Spray Operations 
ideally should have a M.Sc. or Ph.D. in medical -veterinary 
entomology, at least 5 years practical experience in managing a 
major mosquito abatement operation, and a good knowledge and 
understanding of the safe handling and application of 
insecticides . 

Before spraying begins, the Director may be required to 
review draft contracts for aerial application and for the supply 
of insecticide on behalf of the province and to develop detailed 
cost estimates based on final agreements with the suppliers of 
goods and services. 

With the provincial emergency measures organization (EMO) 
representative (usually designated as the Communications Officer) 
and the airport duty officer, the Director of spray operations 
will also assist in locating and assembling the Operations Base 
taking into consideration such matters as a ramp area for the 
aircraft, an area for loading, an area for insecticide storage 
tankers, an area for a field office and meeting room and an area 
for parking vehicles and storing equipment and in determining who 
receives visitor passes and vehicle passes from airport security. 
Also, the airport fire, ramp security and police should be briefed 
as to what will be done at the airport and any potential problems 
associated with the operations. 

Also, all necessary equipment and supplies (detailed below) 
will be requested, including office supplies, safety gear and 
protective clothing, spill control and clean-up materials, special 
maps, portable generator and lights, washroom and emergency 
shower, small tools, and two-way radio and telephone communi- 

137 



cations equipment. 

The aerial applicator will be responsible for the supply of 
all equipment, tools and supplies associated with transferring the 
insecticide from the storage tanks to the aircraft, for fuelling 
the plane and for the maintenance of the aircraft and spray 
systems. They will also be responsible for arranging 
accommodation, food services and transportation for their staff. 

As soon as the cities and towns likely to be sprayed are 
known, the Director will acquire the necessary topographical maps 
for these areas. These will be used to plot the spray blocks. At 
least three copies of each must be prepared. The aerial 
applicator, the public information officer, and the lead 
monitoring agency will each require a copy. The spray blocks will 
be designed in consultation with the aerial applicator. 
Typically, the spray block is square or rectangular (usually 13 x 
13.5 km in size), centred over the community and, includes the 
community and a surrounding buffer zone of about 10 km in all 
directions. From these maps, the applicator can determine the 
longitude -latitude coordinates necessary for programming the on- 
board, computerized, navigation system for each spray block. 

The Director also may be required to attend various meetings 
of the Core Coordinating Committee, the surveillance committee, 
and the various monitoring organizations to brief them on the 
status of preparations being made for spraying and to explain the 
various procedures that will be followed, including the criteria 
for spraying and methods of communication. 

Different tasks may be designated to other members of the 
spray team. The manufacturer's representative may be asked to 
oversee the provisions for storage tankers, the transfer of 
insecticide into them from arriving tanker trucks and out of them 
to the aircraft, spill control, sampling for chemical assays, 
calculating insecticide requirements for each flight and obtaining 
technical information on the insecticide for use by various 
agencies and individuals associated with the health emergency. 
The supervisor of the aerial application crew may be asked to plot 
spray block maps , lead media tours of the aircraft and prepare 
written post- flight summaries. The EMO Communications Officer may 
be asked to open and close the facilities daily, maintain a 
written operations log (noting when personnel arrive and leave the 
site and where they can be reached in an emergency, all deliver- 
ies, spray flight times, telephone calls, etc.) and, of course, 
communicate information to and from the various support groups . 

During the spray operations, the Director, working at the 
Operations Base, will lead a spray team, comprised of himself, the 
supervisor of the aerial application crew (including pilot, 
navigator, and maintenance crew), the technical manager of the 
insecticide manufacturer, and the EMO officer on site. Based on 
biological, meteorological and operational criteria, the spray 

138 



team will decide which of the possible spray blocks should be 
sprayed at any given opportunity. The basis of all such decisions 
should be noted in the written log. 

The Director, as final decision-maker, will issue a work- 
order for each flight and it will proceed as planned, barring 
mechanical problems or last-minute changes in weather conditions 
and he will have this information passed on, through pre-arranged 
channels, to everyone who must be advised. 

Following each flight, the Director will be briefed by the 
aerial application staff on the spray operation, including any 
problems encountered, their observations on wind conditions and 
insecticide drift, etc. 

When the spray operations have been completed, the Director 
will oversee the disassembly of the Operations Base, including the 
applicator's equipment, storage tankers, field office and meeting 
room, etc. An inventory of all remaining equipment, tools and 
supplies should be made. Also, he should assemble all the 
paperwork that was generated during the operations (including the 
log, work-orders, delivery slips, maps of spray blocks, etc.) for 
delivery to the EMO. This information may be vital for the 
province to deal with possible future damage claims. If the 
Director is required to prepare a written report on the operations 
to the Deputy Minister of Health, he should ensure he has a copy 
of all the required documentation should be ensured. 

Equipment 

A variety of equipment is needed at the Operations Base for 
routine, occasional and emergency use. The requirements may vary 
from operation to operation, depending upon the equipment provided 
by the aerial applicator and the EMO. Some of items found 
helpful, if not essential during past operations are listed below. 



Field Office 

The provincial EMO may have a fully- equipped, mobile field 
office available for use. If not, a large construction trailer 
can be rented and equipped with tables, chairs, filing cabinet, 
bookcase, waste -paper baskets, desk trays, clock, lamps, bulletin 
boards, pencil sharpener, calculators, typewriter, photocopier, 
chalk-board, tape-recorder, multiple telephone lines, portable VHF 
transceiver, public address system, pagers, fax machine, and other 
equipment. 

Meeting/Lunch Room 

A second rented construction trailer should be equipped with 
tables, chairs, coffee machine and supplies, cot, bulletin board, 
ashtrays, clock, and any other equipment that might be useful in a 
combined meeting- lunchroom for the operations personnel that are 

139 



working from before dawn until well after sunset every day for 2- 
4 consecutive weeks. 

Protective Clothing and Facilities 

Many items are necessary for safely transferring insecticide 
from arriving transport tankers to the storage tankers and from 
these to the aircraft and for personal hygiene. These items 
include fire extinguishers, first aid kit, rubber-coated apron, 
rubber boots, coveralls, ear-plugs, face-shield, hard-hats, rubber 
gloves, goggles, respirators and cartridges, rain- suits, eye-wash 
station, emergency shower, portable barricades, portable toilet, 
pesticide spill absorption material, and scoop shovels. 

Insecticide Storage/Loading Area 

A variety of tools and equipment are needed in the storage/loading 
area. These include small tools (including mechanic's tool -box, 
metric and imperial socket wrench sets, hammer, pliers, hack-saw, 
vice-grips, wire-cutters, tape-measure, screw-driver set, drum 
plug wrench); stop-watch; polypropylene rope; garbage cans; empty 
drums (with tops removed); padlocks; heavy-duty extension cords 
(various lengths); mechanic's light; portable outdoor lighting; 
insecticide transfer pumps, hoses, couplings, filter, cartridges, 
and spare parts (usually provided by the aerial applicator) ; a 
rented, 40,000 L capacity, compartmentalized, tanker -trailer unit 
for the bulk storage of insecticide, kept for the duration, with 
wooden-crib supports. 

Supplies 

Many different materials are used during the emergency spray 
operations. These are categorized below. 

Field Office 

Office supplies, including pencils, pens, chalk, markers, 
high- lighters, rulers, yardsticks, dividers, compass, erasers, 
rubber bands, paper-clips, transparent tape, masking tape, 
electrician's tape, file folders, legal and 22x28 cm envelopes, 
carbon paper, archive boxes, 2 -way memos, typewriter correction 
fluid, 22x28 cm paper, note-pads, clip-boards, 3-ring punch, 3- 
ring binders, staplers, scissors, utility knife, date stamp, ink 
pad, calenders, thumb tacks, message pads, long-distance record 
pads; telephone directories (city, province, provincial 
government); dictionary; maps, including topographical maps, 
provincial highway maps, and city street maps; maintenance 
supplies, including broom and dustpan, cleaning rags, paper 
towels, window cleaner, and garbage bags; thermos water- jugs; 
flash-lights and spare batteries. 



140 



Insecticide 

Insecticide should be delivered by tanker truck directly from 
the manufacturer to the Operations Base. The first trailer units, 
with a combined storage capacity of at least 40,000 L and kept as 
storage tanks for receiving future shipments, must be properly 
sited and supported. Sufficient insecticide should be ordered to 
treat the spray blocks for all known communities at risk. 
Additional insecticide should be ordered as soon as new 
communities are added to the list. 

Inventories of Personnel, Equipment and Supplies 

Much time will be saved if resource lists are up-dated 
annually by the EMO or some other designated agency for operations 
personnel. The most important such listings are given below. 

Suppliers of Services, Materials and Equipment (supplier's 
name, address, telephone numbers [working and non-working hours], 
fax numbers, type of equipment/supplies/services, quantity on hand 
or time required to produce/obtain and supply) . 

Resource Personnel in Government, Universities, and Business 
(including the names, addresses, and telephone numbers of 
professionals, technical experts, operations personnel, etc.). 

c. Planning and Scheduling 

Contingency plans may have been prepared for a provincial 
health emergency. If so, various committees probably have been 
established, if only one paper, to deal with the emergency. An 
emergency involving in outbreak of mosquito -borne encephalitis may 
or may not fit into an existing general health emergency plan. In 
any case, a coordinating committee, composed of the relevant 
departments will lead and direct the various surveillance and 
vector control activities. 

In the case of a mosquito-borne encephalitis outbreak, this 
lead committee (which may be called the Core Coordinating 
Committee or Task Force or something else) will probably consist 
of the Deputy Ministers and Ministers of Health, Emergency 
Measures, Environment and Agriculture. Key professional staff 
will report to them (occasionally or regularly, directly or 
through their Deputy Minister) during the emergency. These staff 
may include the chairpersons of the surveillance and monitoring 
committees, the provincial epidemiologist, the director of the 
provincial diagnostic laboratory, the provincial entomologist, the 
provincial veterinarian, the public information coordinator, the 
director of purchasing, the EMO coordinator, the provincial 
solicitor, etc. 

Regardless of the reporting system, this lead committee will 
require complete up-to-date information and recommendations each 
time it meets. It will be under pressure to make decisions which 
may or may not be popular to the public, the media, environmental 

141 



groups, professionals, etc., which may have major health, 
economic, social, and political consequences. Thus, this lead 
committee depends on the best professional, scientific and 
practical advice that is available to it. 

At the beginning, the lead committee will be deciding on who 
will be responsible for doing what and when it should be 
available. Appointments to key temporary positions will be made. 
Authority will be given to acquire vector control equipment and 
supplies, escalate surveillance activities and diagnostic 
services, organize monitoring programs, develop an emergency 
public information program, second staff, call back key personnel 
from vacation leaves, etc. Obviously, during the first few days 
at least, the activities of this committee and the people 
supporting may appear chaotic. The success of the lead committee 
will be entirely dependent on how well the members of the 
committee and the people working with them interact. Much will 
depend on the leadership abilities of the Minister of Health and 
the Deputy Minister. 

Based on the information and advice given to them, the lead 
committee will oversee the emergency surveillance, public 
information and vector control programs. They will decide which 
communities should be sprayed and direct the operations group to 
do so as quickly and safely as possible. The spray operations 
group will be expected to develop a tentative spray schedule, 
based on the lead committee's priorities, usually the largest and 
closest population centre first and the smallest and most distant 
last if the incidences of disease are distributed throughout a 
given region of the province. 

Changes in scheduling the individual spray blocks will be 
unavoidable if the spray operations are to take advantage of any 
opportunities that local weather conditions permit. One should 
not be waiting around to spray one town because of poor weather 
conditions if spraying conditions are good over another town. 
Changes in plans may make the work of the support groups 
difficult, if not impossible, at times but the key concern should 
be the protection of as many people as possible as soon as 
possible. 

Additions to the initial list of towns and cities at risk 
should be expected, especially if the emergency was recognized 
relatively early. Additional supplies will have to be acquired, 
spray block maps drawn, and so on. 

d. Legislation and Jurisdiction 

From a legal and jurisdictional point-of-view, dealing with 
an outbreak of mosquito -borne encephalitis within a given province 
is that province's responsibility. If it does not have the 
resources to cope with the problem, it can call upon the federal 
government for assistance. Usually, some of the resources are 

142 



available and those that are not can be obtained fairly readily 
from other jurisdictions through existing provincial and federal 
cooperative agreements. Depending upon the scope of the emergency 
and the costs incurred, the province may be eligible for federal 
aid. 

From a vector control point-of -view, several legal matters 
must be considered. These include the official declaration of a 
provincial health emergency (and, later, its termination), the 
waiver of those sections of any provincial Acts or regulations 
that might prevent the province from implementing a large -area, 
aerial application of insecticide for vector control, adherence to 
the federal Pest Control Products Act and its regulations, respect 
for the International Migratory Birds Convention, the waiver of 
federal aviation regulations governing low- level flights over 
populated areas and within air traffic control zones , the 
successful negotiation of contracts with major suppliers of goods 
and services , and the approval of funds for emergency 
expenditures. The lead committee, Spray Operations Director, EMO 
Coordinator and provincial solicitors will have to ensure that all 
these matters are finalized before spraying begins. 

The declaration of a health emergency enables all the other 
legal matters to be considered. A formal emergency declaration is 
usually made by the Minister of Health on the advice of provincial 
health officials and the disease surveillance committee. The 
basis of such a recommendation to the Minister is a combination of 
known virus and vector activity and suspected or confirmed cases 
of the disease with an expectation that the health situation will 
deteriorate unless there is intervention. This declaration will 
reinforce the vector control authority of the Minister and serve 
to activate various support and assistance agreements with other 
government departments (provincial and federal) . 

After considering the findings and recommendations of the 
surveillance committee, the first decision of the Minister is 
whether or not the situation requires a formal declaration. If 
so, the Minister will advise and consult with other Ministers of 
Cabinet, including the Attorney-General and the Minister 
responsible for Emergency Measures. The necessary papers will be 
prepared for the Minister to formally declare a health emergency. 

Similarly, when the surveillance committee and/or provincial 
epidemiologist consider the health emergency to have passed, the 
Minister will be advised to formally declare the health emergency 
to be terminated. Usually, this will occur soon after the vector 
control program has been completed and no further human cases have 
been detected. 

e. Procedural Guidelines 

Several key operational procedures , which have been developed 
during past spray operations and may serve as guidelines for 

143 



future emergency vector control operations, are outlined below. 

Estimating Insecticide Requirements 

Knowing the names of the cities and towns that will be 
sprayed, topographical maps can be used to draw spray blocks 
encompassing each of these communities. Most of the population 
centres will be small. A 13x13.5 km spray block will protect 
these centres. The area of such a block is 17,550 hectares 
(43,348 acres) . 

Some blocks (e.g. those of larger cities or those with 
unusual terrain) may be rectangular or irregular in shape. The 
important point is to ensure that an adequate buffer zone 
surrounds the community. 

Knowing the insecticide and the approved application rate, 
the quantity of insecticide required can be calculated. Adding up 
the insecticide requirements for all of the spray blocks and 
allowing an extra 500 litres for insecticide remaining in transfer 
pumps, hoses and filters and the bottom of spray tanks, the 
insecticide requirements can be estimated. 

For example, if the total area of the spray blocks was 
500,000 hectares and the insecticide was applied at 0.4385 L / 
hectare, one would need 219, 250 L for the treatments. 



Storage of Insecticide 

Bulk insecticide will be shipped by truck, directly from the 
manufacturer's formulation plant to the Operations Base, in tank 
trailers. Tankers are required to store the arriving insecticide. 
From past experience a storage tank capacity of at least 40,000 L 
is essential. One large or 2 smaller tank trailers meet this 
requirement. Three spray blocks could be treated with this amount 
of stored product. Usually, the first one or 2 tankers to arrive 
are used for this purpose until they can be rented locally. While 
the insecticide in these storage tanks is being used in the vector 
control program, additional supplies will be en route. 

Ideally, such tanks should have both ends sloped to provide 
fast drainage, a 4-compartment manifold with a 7.5 cm gate valve 
outlet allowing curbs ide discharge and mechanical emergency valves 
and operator in the cabinet. 

Such storage tankers must be situated adjacent to the 
aircraft's parking position for easy loading. They must be 
properly positioned and then reinforced with heavy timbers or 
supported by a multi -wheeled trailer dolly for safety reasons. 

Transferring Insecticide from Delivery to Storage Tanker 

The driver of the delivery truck will usually handle the 
transfer of material from his tanker to the storage tanker with 
the assistance of operations personnel. 

144 



Before the transfer begins, someone knowledgeable in the safe 
operation of tanker trailers should be responsible for ensuring 
the following: inspecting the storage tanker to ensure that it has 
sufficient room available to accept the full load being delivered; 
blocking the wheels of the tanker; grounding the tanker; ensuring 
the transfer hoses are in good repair, sufficient lengths of hose 
are available, and all connections are secure; ensuring the tanker 
vent is present or the lid is open and that the bottom valve is 
closed; ensuring that everyone involved is wearing all necessary 
protective clothing and that the spill control tools and supplies 
are on hand; ensuring, if filling is being done through the open 
top lid, that the insecticide transfer hose has been securely 
fastened in place using heavy wire. 

A delivery/transfer record form should be completed, 
detailing the shipment number, the supplier, the carrier's name, 
the driver's name, the shipment tanker number, the storage tanker 
number, the date and time transfer occurred, the weigh bill 
number, the personnel involved in the transfer, and a description 
of any spills and actions taken to clean-up the spills. 

Transferring Insecticide from Tanker to Aircraft 

The aerial application crew will locate and assemble the 
transfer pumps, liquid meter, filter unit, hoses, and related gear 
needed for loading. Insecticide is transferred through 7 . 5 cm 
reinforced hose equipped with quick- couplers . Two pumps with a 
capacity of 900 L per minute, are connected in tandem to the 
tanker. Next, a metering device, calibrated for the insecticide 
to be used, is linked by hose to the pumps. Then, an upright 
filter canister is employed to filter out any particulate 
contamination. Lastly, a long hose is attached to the intake 
valve of the aircraft. 

Before loading the aircraft, ensure the vents or top lid is 
open on the storage tanker to prevent the tanker walls from 
collapsing under vacuum. Before opening the emergency valves, 
ensure all hoses are properly connected at both ends. In case of 
emergency, the emergency valves may be closed by operating the 
remote controller located at the front end of the tanker. 

Four persons are needed for loading. One person for relaying 
signals from the ground crew to the aerial crew, one person on- 
board for monitoring liquid levels in the on-board spray tanks, 
and two people for opening and closing valves, starting and 
stopping pumps, monitoring the meter and disconnecting and moving 
hoses from the aircraft. 

In this fashion, sufficient insecticide for one small spray block 
(about 9000 L ) can be pumped on-board in 11 minutes. 

Preparation of Spray Block Maps 

Often, several topographical maps must be pieced together to 

145 



have a sheet on which the spray block can be drawn. The National 
Topographical Series is used at a scale of 1:50,000 (1 cm - 0.25 
km). In Manitoba, these maps are available from the Maps Sales 
office of Manitoba Natural Resources. Features important to the 
aerial application including population centres, roads, forests, 
swamps, water bodies, reservoirs, contour lines, transmission 
lines, rail -roads, and towersare all present on the map. Because 
3 finished sets of spray block maps are needed, the maps are best 
prepared in a room with adequate table space. 

The 3 sets will be used by the pilots (these are considered 
the originals for legal purposes), the EMO (including the public 
information officer) and monitoring/assessment agencies. The 
originals will have annotations made on them pertaining to the 
aerial application, including flight times and date, any 
observations made by the pilots, start and finish points, the 
flight line and directional sequence followed, etc.). They should 
be provided to the EMO after the operations are complete. 

If original maps from previous emergency spray programs are 
available when the current emergency is declared, they should be 
provided to the Spray Operations Director to facilitate the 
preparation of new maps . 

A legend should be given for each spray block map including 
name of the community, date and time sprayed, load number, 
waypoint coordinates and line numbers. The map itself will have 
the flight lines (drawn in a North-South direction) that will be 
followed by the spray plane. Depending on wind direction when the 
plane arrives over the spray block, spraying may start on either 
side of the spray block. Usually, the navigation system is set to 
2 points on the east side of the spray block (the NE and SE ends 
of the first flight line, usually marked '8' and '7', 
respectively). These 2 points are called 'waypoints' and are used 
to determine precise latitude- longitude coordinates for setting 
the computerized navigation system (i.e. an inertial navigation 
system such as the Litton LTN-51 or a Loran system such as the 
Texas Instruments TI 9100) . 

A typical spray block for a small rural town is 13x13.5 km 
allowing about a 6.5 km buffer zone around the community. This 
design minimizes mosquito movement into the community after 
spraying takes place and allows for some displacement of the 
actual block sprayed due to droplet drift with wind. Larger 
cities will usually require an irregularly- shaped design, 
reflecting their uneven growth in different directions. 

The typical 13x13.5 km block provides for 17 N-S flight lines 
13 km in length and 0.8 km apart. The N-S line orientation 
provides for a cross-wind component necessary for spray droplet 
dispersal and drift. Thus, spray flights can never be flown when 
the winds are coming from due N or due S. (This was not a serious 
operational problem in August during 1975, 1977, 1981, or 1983, 

146 



in Manitoba, because the wind was not directly N nor directly S 
for very long. ) 

General Record-Keeping 

Difficult as it is to recognize and make notes on every 
significant meeting that is attended, activity that takes place, 
event that occurs, and telephone call that is made at the 
Operations Base, it must be done. The key personnel (including 
the Spray Operations Director, manufacturer's representative, 
aerial crew supervisor, and EMO Communications Officer) should 
each maintain chronological records of everything they do and 
discuss with others. For everyone's benefit, these people should 
meet daily to review what has happened in the last 24 hours and 
what plans have been made for the remainder of the spray 
operations. Each person can update the others on significant 
points for them to record. Their records will prove invaluable to 
themselves and their organizations after the emergency program is 
finished for financial, legal, and technical reasons. 

Every receipt, delivery slip, work-order, expense claim, 
requisition, purchase order, invoice, memo, letter, report, spray 
block map, etc. must be properly noted, organized and provided to 
the appropriate support group. Such details are usually handled 
by the Communications Officer. 

f. Reporting Procedures 

Each province may have its own reporting procedures , 
depending upon how it has organized itself to respond to an 
outbreak of mosquito -borne encephalitis. Even approved 
contingency plans can be expected to change, depending upon the 
policies of the government responsible, the senior administration, 
the social and economic climate. However, reporting lines and 
procedures should be made known to everyone as soon as possible to 
avoid possible personal or government embarrassment. 

Typically, the surveillance committee will report to the 
Deputy Minister of Health through its chairperson. The operations 
personnel likely also will report directly to this senior 
administrator through the Director of Spray Operations. The 
Deputy Minister will report, in turn, to the Minister of Health. 
Monitoring groups, made up of professionals from various organiza- 
tions and levels of governments, will likely be organized by the 
Deputy Minister of Environment and will report their findings to 
that office. The Deputy, of course, will report to the Minister. 
These and supporting Ministers may form the Core Coordinating 
Committee or Emergency Task Force and will make recommendations to 
or be empowered by the Provincial Cabinet. Although these or 
similar channels may be established, one should expect changes to 
occur or informal channels to form over the course of the 
emergency program. Whatever official channels are established, 

147 



the emergency personnel would be well-advised to follow them 
carefully. 

During the emergency, everyone involved, regardless of their 
level in the temporary organization, will need to be kept up-to- 
date, if not up- to-minute, on all significant findings, 
occurrences, and activities within their area of responsibility 
and will be required to summarize and pass on this information 
and/or recommendations to the person to whom they report. 
Periodically, especially if the emergency operations are lengthy, 
they also may be required to provide reports to the various 
committees. After the emergency is over, they may have to prepare 
written reports on the activities of their group, highlighting 
significant data, activities, expenses, etc. Possibly, the 
reports of the various organizations, agencies, groups, and 
individuals may be presented at a special symposium or published 
in a government document. Also, some documents will be required 
for legal purposes. For these reasons, the need for complete and 
accurate records and reports and the need for following official 
reporting procedures is obvious . 



148 



3. PUBLIC INFORMATION 

a. Implementation 

The timely provision of complete and accurate information on 
the status of the mosquito -borne disease involved, the vector 
control measures planned, and on personal protection is necessary 
to maintain public support of the emergency measures being taken. 
A well-respected public information officer should be appointed to 
coordinate the distribution of information being provided to the 
public - through both the news media and telephone inquiry lines. 
During an encephalitis outbreak, the information coordinator and 
their staff release information on disease surveillance and 
control on a daily basis. 

As soon as disease surveillance indicates the possibility of 
a mosquito -borne encephalitis outbreak, the public information 
program should start. Initially, this may entail the information 
coordinator being briefed on the activity levels of the virus and 
mosquito vectors and any concerns that provincial health offic- 
ials may have that an outbreak may occur. 

By involving the information coordinator early, that person 
is enabled to review contingency plans for dealing with an 
encephalitis outbreak. Steps can be taken early to update 
resource files, contact lists, and operational requirements. 
Colleagues available for help during natural disasters may be 
alerted in turn. Further, as an outbreak becomes imminent, the 
information coordinator may begin to attend meetings of the 
surveillance committee and of health officials to gain a better 
understanding of the ongoing surveillance and planned control 
program and to prepare additional draft press releases on all 
aspects of these interrelated programs. 

Alerted to the possibility of an outbreak, the coordinator 
may be asked to draft press releases on such topics as personal 
protection from mosquito bites and the status of disease 
surveillance for issuance by the Minister of Health. Emphasis 
should be placed on the escalated surveillance program and the 
importance of the public protecting themselves from mosquito 
bites. Depending on the government's position on emergency 
mosquito control, the steps that are under consideration (should 
the situation deteriorate) may be outlined in the initial 
statement. 

By the time a health emergency is declared, the information 
coordinator will have organized a facility for an emergency 
telephone inquiry service, complete with telephones, desks, 
chairs, map boards, chalk boards, office equipment and supplies, 
and a coffee -maker . Separate telephone lines should be available 
for the public, for the media and for internal communication. 

Trained professionals should answer the phones. The chosen 
professionals will likely include public health nurses, medical 

149 



entomologists, agronomists, wildlife biologists, and apiarists who 
have good public relations skills and can readily assimilate 
detailed, technical information on all aspects of the disease 
surveillance and control programs. 

Assuming a detailed, information package on the biology and 
control of the mosquito -borne disease has been prepared by the 
information coordinator and approved by professional health and 
vector control officials, this information could be distributed to 
the media and local government officials early in the public 
information program, smoothing the way for subsequent information 
releases. 

b. Maintenance Requirements 

Preparation is the key to a good public information program. 
An information coordinator should only have to update the basic 
information files once alerted to a possible outbreak of mosquito- 
borne encephalitis. Neither the government, the media or the 
public will understand or accept the emergency program if the 
public information program fails through lack of advance 
preparation. 

Requirements During Non- epidemic Years 

Some of the information maintained between outbreaks is 
similar to that which would be periodically updated to deal with 
any emergency situation, natural or otherwise. Other information 
may be specific to mosquito -borne encephalitis. The basic 
requirements are outlined below. 

Compendium of Questions/Answers 

Ideally, the information coordinator will have developed an 
information manual for use by the professionals fielding questions 
from the public through the telephone inquiry line. If an 
outbreak of mosquito -borne encephalitis has occurred at some time 
in the past, the questions that the public (and media) will 
undoubtedly ask will be apparent from a review of old press 
clippings, publications (e.g. Donogh 1976; Anon. 1976, 1978; Mahdy 
et al. 1979) and administrative and consultant reports (e.g. Anon. 
1983). 

Some of the answers may also be obvious. However, many 
questions may not have been adequately answered in the past. 
Either they were poorly articulated or understood or current 
surveillance and control methods and materials make the past 
answers obsolete. However, anticipating the questions, the 
information officer can quickly contact his network of experts to 
obtain accurate, factual, up-to-date answers. Thus, he can 
prepare good responses to the flood of calls that the inquiry line 
will receive. 

Many of the technical questions will revolve around the human 

150 



safety and environmental impact of the insecticides used. It 
would be difficult, in a manual such as this, to attempt to answer 
all the possible questions that might be asked about the dozens of 
different mosquito control products that might be used alone or in 
combination during a vector control program. However, it would be 
useful to list the more -commonly asked questions. 

Once it has been decided which insecticide(s) will be used 
during the health emergency, the answers, specific to those active 
ingredients, can be developed with the assistance of technical 
resource people. 

Some of the more commonly asked questions follow: 

how safe is this insecticide to me, my children, my pets? 
what is the insecticide being sprayed? 
who manufactures, sells, distributes the insecticide? 
was this insecticide used as a nerve gas during the war? 
wasn't this insecticide banned in the U.S.A.? 
on what other insects is this insecticide registered for use? 
will all the bees, butterflies, lady bugs, dragonflies, be 
killed? 

what other products could have been used in the larviciding, 
adulticiding? 

why was this product chosen over the others available? 
is this insecticide safe to the environment? 
will it kill nestlings, insect-eating birds? 
if sprayed over rivers, will it kill the fish? 
is it safe to eat the vegetables, fish, birds, that have been 
sprayed? 

can I, my kids, my pet be outdoors during the spraying? 
will this insecticide harm the paint/finish on my car? 
does this insecticide cause cancer? 
will this chemical aggravate my asthma, bronchitis, allergies? 

The answers to some questions cannot be prepared in advance. 
These include queries on precisely when and where vector control 
will be carried out during any given day. The information 
coordinator must obtain updates on such matters every few hours , 
recognizing that changing weather conditions may drastically alter 
vector control plans from hour to hour. Because most of the calls 
received will centre on the question, "When is spraying planned 
for my community?", this makes the task of rapidly transferring 
updated spray schedules a challenge. Also, there will be some 
questions of a technical nature that either cannot be anticipated 
or adequately answered by personnel manning the telephones. The 
information coordinator then must attempt to obtain the precise 
answers from the experts who do know and relay this information 
back to the original caller. The specific question/ answer can 
then be added to the compendium. 

151 



List of Technical Resource Persons 

As noted above, some questions cannot be anticipated. Thus, 
it is vital that the information coordinator maintain a network of 
professional contacts to whom he can turn when answers are needed 
quickly. 

The listing would include the names , addresses and telephone 
numbers (day and night) of other information officers. These 
people might include colleagues in federal, provincial and 
municipal departments across Canada. During an emergency, these 
persons, in turn, may be able to obtain needed technical 
information through professionals in their respective departments. 

In addition, the listing would include professionals in 
provincial and municipal departments of health, environment, and 
agriculture who have valuable knowledge and experience in fields 
related to disease surveillance and control. Many of these 
individuals will likely already be involved, directly or 
indirectly, in dealing with the outbreak. 

Lists of Contacts 

Various contact lists can be developed by the information 
coordinator for use during the encephalitis outbreak. The 
contacts who are listed will vary from province to province and 
from year to year. Computerizing such lists will facilitate 
scheduled revisions. 

Media Contacts 

Because the public information program is dependent on the 
news media to provide up-to-the-minute information to the public, 
it is very important that contacts be established with all the 
news-rooms of major radio and television stations and newspapers 
in the province . 

Such contact lists (complete with names, addresses and 
telephone numbers) must be updated frequently to remain current 
and to reflect changes in the organizational structure of the 
firms and staff. 

From public awareness surveysit has been shown that 
television news is the most effective means of disseminating 
information to the general public. If any compromises must be 
made, it should not include this medium 

Local Officials 

Lists of municipal and regional contacts may also prove 
useful during the health emergency. Knowing who the local mayors, 
reeves, MLA's and MP's are may be helpful, especially when there 
communities are locations where human/horse cases have been 
observed and/or which will be aerially sprayed. Early 
notification of these very important people may be vital to local 

152 



community support. 

In addition, it may be helpful to develop special lists of 
contacts for each community that may be involved in the vector 
control operations. The lists might include local public health 
nurses, medical doctors, veterinarians, airport managers, RCMP 
detachments, etc. 

Health Officials 

Although it will not normally be necessary for the 
information coordinator to contact surveillance officials in other 
jurisdictions, this being done regularly by local surveillance 
personnel. The following contacts, current in 1989, may prove 
useful: 

Municipal 

Winnipeg 

Dr. Doug G. Luckhurst 
City of Winnipeg 
Health Department 
280 William Avenue 
Winnipeg, Manitoba R3B 0R1 
(204) 986-2415 



Provincial 
Ontario 

Dr. Gordon Surgeoner 

Department of Environmental Biology 

University of Guelph 

Guelph, Ontario NIG 2W1 

(519) 824-4120 

Manitoba 

Dr. Lyla Sekla 

Manitoba Health Services Commission 

Cadham Provincial Laboratory 

750 William Avenue 

Winnipeg, Manitoba R3C 3Y1 

(204) 944-0270 

Dr. Margaret V. Fast 
Manitoba Health 
Preventive Medical Services 
831 Portage Avenue 
Winnipeg, Manitoba R3G 0N6 
(204) 945-6834 



153 



Saskatchewan 

Dr. Roy West 

Saskatchewan Health 

3475 Albert Street 

Regina, Saskatchewan S4S 6X6 

(306) 565-7408 

Alberta 

Dr. John R. Waters 

Alberta Social Services and Community Health 

Seventh Street Plaza 

Edmonton, Alberta T5J 3E4 



Federal 



Dr. Harvey Artsob 

National Arbovirus Reference Service 

University of Toronto 

Banting Institute 

100 College Street 

Toronto, Ontario M5G 1L5 

(416) 978-6704 



U.S. CDC 

Dr. D. Bruce Francy 

US Health and Human Services 

Public Health Service 

Centers for Disease Control 

Center for Infectious Diseases 

P.O. Box 2087 

Fort Collins, Colorado 90522-2087 

(303) 221-6432 

U.S. State Surveillance Officials 
Iowa 

Dr. Wayne Rowley 
Department of Entomology 
Iowa State University 
Ames, Iowa 50011 
(515) 294-1572 

Minnesota 

Dr. Robert Sjogren 

Metropolitan Mosquito Control District 

2380 Wycliff Street 

St. Paul, Minnesota 55114 

(612) 645-9149 

154 



Dr. Michael Osterholm 
Minnesota Department of Health 
717 Delaware Street Southeast 
Minneapolis, Minnesota 55440 
(612) 623-5414 

South Dakota 

Kenneth A. Senger 

Epidemiology 

South Dakota Department of Health 

Joe Foss Building 

Pierre, South Dakota 57501 

(605) 773-3364 

North Dakota 

Robert Hennes 

Division of Environmental Sanitation and Vector Control 

North Dakota State Department of Health 

State Capital Building 

Bismark, North Dakota 58505 

Veterinarians 

Lists of practising veterinarians in any given province can 
be obtained from the Agriculture Department, usually the 
provincial veterinarian or senior pathologist. Such contacts may 
be helpful in helping TV News film crews obtain footage of such 
visual elements as, for example, horse vaccinations. 

c. Assessment 

A follow-up assessment of the effectiveness of public 
information is important. In order to improve future such 
programs, it is worth assessing the various components of the 
latest program. Few such evaluations have been carried out for 
public information programs developed for outbreaks of mosquito- 
borne encephalitis. 

One such study was carried out after the 1983 encephalitis 
outbreak in Manitoba (Anon. 1983) . The consultant assessed public 
perceptions of the health risk presented by WEE, public 
perceptions of the aerial spraying program, the relative 
effectiveness of the different media used in the awareness 
campaign, the public's comprehension of the message elements and 
any behaviourial impact the campaign produced. It was concluded 
that the objectives of that public information program were met, 
in general, but that a significant number of Manitobans did not 
act on advice to avoid mosquito bites and to avoid exposure to the 
insecticide spray. 

Such weaknesses in the information program, especially 

155 



failing to induce people to protect themselves by wearing mosquito 
repellents when they are outdoors, underline the need for 
continual improvement. 



156 



PART III 



157 



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Population ecology of Culex tarsalis (Diptera: Culicidae) in 
a foothill environment of Kern County, California: temporal 

184 



changes in female relative abundance, reproductive status and 
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185 



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187 



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188 



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189 



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190 



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191 



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possible mortality factor. Bull. Wildl. Dis. Assoc. 5: 248- 
253. 

Zinkl, J.G., J. Rathert, and R.R. Hudson. 1978. Diazinon poisoning 
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Zweighaft, R.M. , C. Rasmussen, A. Brolnitsky, and J.C. Lashof. 

1979. St. Louis encephalitis: the Chicago experience. Am. 
J. Trop. Med. Hyg. 28: 114-118. 



192 



APPENDIX I 
INSECTICIDES COMMONLY USED IN MOSQUITO CONTROL PROGRAMS IN CANADA 

This appendix provides information (1) on the insecticides 
that are commonly used in municipal mosquito abatement programs in 
Canada, and (2) on the repellents available for personal use and 
for use on livestock to protect against mosquito bites. 

Although there are several hundred pest control products 
registered for use against mosquitoes in Canada, most of these 
products are for the home-owner. Relatively few insecticides are 
used in routine mosquito abatement programs. The products listed 
below have been extracted from an all-inclusive listing provided 
by the Pesticides Directorate of Agriculture Canada. They are 
only examples of those that have been or are being used for large- 
scale mosquito control programs. A complete pest control product 
listing is beyond the scope of this manual. 

The 3-letter code at the beginning of each line refers to the 
registrant. The names and addresses of these registrants are 
given in Appendix 3. The number following each registrant's code 
is the Pest Control Products Act registration number. 

TEMEPHOS 



KEM 
KEM 
SAF 
SAF 



13694.00 
13695.00 
15567.00 
16460.00 



RIDDEX ABATE 4E 
KEMSAN ABATE 2-G 
SANEX ABATE 2G 
SANEX ABATE 4E 



PROPOXUR 

CHH 11029.00 BAYGON U-L-V SPRAY INSECTICIDE 

CHH 11313.00 BAYGON OSC INSECTICIDE 

CHH 13212.00 BAYGON MOS INSECTICIDE 

CHH 13934.00 BAYGON INSECTICIDE READY-TO-USE IN THERMAL 

FOGGERS 
CHH 14826.00 BAYGON READY-TO-USE INSECTICIDE 
CHH 16069.00 BAYGON 200 READY-TO-USE ULTRA LOW VOLUME 

INSECTICIDE 
SAF 15565.00 SANEX PROX-120 ULV CONCENTRATE 

BACILLUS THURINGIENSIS ISRAELENSIS (BTI) 



ABT 


18158 


.00 


VECTOBAC- 


•200 


G 


ABT 


19455 


.00 


VECTOBAC 


600 


L 


ABT 


19466 


.00 


VECTOBAC 


200 


G 


DUP 


19220 


.00 


BACTIMOS 


G 





193 



ZOE 19241.00 


TEKNAR HP-D 


ZOE 19239.00 


TEKNAR G 


CHLORPYRIFOS 




DOW 10636.00 


DURSBAN*2E 


DOW 10637.00 


DURSBAN*4E 


DOW 12223.00 


DURSBAN 2 1/2 G 


MALATHION 





CGC 


12590. 


00 


CHP 


11591. 


00 


CYC 


9337. 


00 


DIS 


13883. 


00 


DIT 


9975. 


00 


EMO 


18322. 


00 


GAX 


8624. 


00 


GAX 


16198. 


00 


GRA 


15380. 


00 


INT 


5821. 


00 


INT 


8480. 


00 


KEK 


18184, 


00 


KEM 


9920. 


00 


KEM 


12216, 


,00 


KEM 


15994 


,00 


SAF 


6022 


,00 


SAF 


9947 


,00 


SAF 


16099 


.00 


UAG 


19364 


.00 


METHOXYCHLOR 


CGC 


10481 


.00 


CHP 


10603 


.00 


GRA 


15382 


.00 


GRX 


16208 


.00 


INT 


13558 


.00 


INT 


18088 


.00 


KEM 


19172 


.00 


LAT 


10690 


.00 


MBY 


14772 


.00 


SAF 


12733 


.00 


STD 


11617 


.00 


UAG 


13727 


.00 



MALATHION 500 EC 

CHIPMAN MALATHION 500 

CYTHION LIQUID INSECTICIDE PREMIUM GRADE 

MALATHION 

MALATHION 50 

MALATHION 50E EMULSIFIABLE LIQUID INSECTICIDE 

M-50 EMULSIFIABLE CONCENTRATE 

GARDEX 50% MALATHION EC INSECTICIDE 

GARDEX MALATHION ULV CONCENTRATE 

GREEN LEAF MALATHION 50% EC INSECTICIDE 

CO-OP MALATHION 500 EC INSECTICIDE 

CO-OP MALATHION INSECT SPRAY 

VANQUISH EMULSIFIABLE CONCENTRATE 

RIDDEX MALATHION 500 EC EMULSIFIABLE 

CONCENTRATE 

RIDDEX CYTHION ULV INSECTICIDE 

RIDDEX MALFOG 45 FOGGING INSECTICIDE 

SANEX MALATHION 50M 

SANEX DYNA-FOG M-L LIQUID INSECTICIDE 

SANEX MALATHION 50 EC 

CLEAN CROP MALATHION 50% EC INSECTICIDE 



METHOXYCHLOR 240 EC 

CHIPMAN METHOXYCHLOR SPRAY CONCENTRATE 

INSECTICIDE 

GREEN LEAF METHOXYCHLOR 25% EC INSECTICIDE 

METHOXYCHLOR 240 

CO-OP METHOXYCHLOR 25 EC INSECTICIDE 

IPCO METHOXYCHLOR 25% EC 

KEMSAN METHOXYCHLOR 240 EC INSECTICIDE 

LATER' S METHOXYCHLOR 25% EC INSECTICIDE 

METHOXOL 240 -EC 

SANEX MOXY GARDEN SPRAY CONCENTRATE 

METHOXYCHLOR 2.4 EC INSECTICIDE 

CLEAN CROP METHOXYCHLOR 240 



194 



METHOPRENE 



ZOE 
ZOE 



13797.00 
15152.00 



PYRETHRINS 
ABE 9836.00 



ALTOSID SR-10 INSECT GROWTH REGULATOR 
ALTOS ID BRIQUET MOSQUITO GROWTH REGULATOR 



WACO TOSSIT PYRETHRUM FORMULA TO KILL MOSQUITO 
LARVAE 



RESMETHRIN 
PEI 15187.00 



SBP-1382 MOSQUITO FOG - 40% 



2. REPELLENTS FOR PROTECTION OF PEOPLE & LIVESTOCK 



Several hundred repellents are registered in Canada for 
protecting humans, pets and livestock (including horses) from 
mosquito bites. Available space does not permit the listing of 
all such pest control products. The presence or absence of a 
product on this listing does not constitute endorsement or 
otherwise. The examples of repellents given below are used only 
to illustrate the active ingredients, types of formulations, 
target users, and manufacturers involved. 

The repellents listed are sorted by active ingredient. The 
3 -letter code at the beginning of each line signifies the 
registrant. The number following the 3 -letter code is the Pest 
Control Products registration number. Some repellents are listed 
under several active ingredients because the formulations contain 
2 or more active ingredients. The names and addresses of the 
registrants are given in Appendix III. 



OIL OF CITRONELLA 



DTC 
MCO 
MRA 
MRA 
NEW 
NEW 



8719.00 
1526.00 
18500.00 
20779.00 
18682.00 
18780.00 



CERTIFIED CITRONELLA OIL INSECT REPELLENT 

REPALFLY MCKIRDY'S SPECIAL FLY REPELLENT 

X-IT INSECT REPELLENT 

X-IT INSECT REPELLENT STICK 

V-TO ROLL ON CITRONEL MILK 

V-TO PUMP SPRAY CITRONEL MILK 



195 



DIMETHYL PHTHALATE 



JBL 


15433 


.00 


MCO 


1526 


.00 


MLS 


18364 


.00 


MLS 


18365 


.00 


MLS 


18366 


.00 


MRA 


20779 


.00 


NOZ 


12401 


.00 


NOZ 


12402 


.00 



BF-100 BLACK FLY REPELLENT 

REPALFLY MCKIRDY'S SPECIAL FLY REPELLENT 

CUTTER EVERGREEN SCENT INSECT REPELLENT 

CUTTER INSECT REPELLENT 

CUTTER EVERGREEN SCENT INSECT REPELLENT CREAM 

X-IT INSECT REPELLENT STICK 

NOXEMA INSECT REPELLENT LOTION 

NOXEMA TAN & GUARD LOTION 



DEET PLUS RELATED ACTIVE TOLUAMIDES 



AFY 
AIG 
AMW 
AMW 
ARE 
ARE 
ARI 
AVM 
BDC 
BOY 
BOY 
CCN 
CCN 
CGC 
CGC 
CHZ 
COS 
DEV 
DFT 
DFT 
FFL 
FUB 
GUC 
HOH 
INT 
INT 
JOH 
JOH 
JOH 
JOH 
JOH 
JOH 
JOH 
JOH 



20846.00 
14333.00 

9154.00 
14811.00 
17746.00 
18726.00 
19018.00 
16638.00 
18399.00 
17956.00 
17957.00 
18040.00 
20774.00 

4039.00 
12958.00 
16811.00 
18400.00 
16818.00 
19107.00 
19194.00 
18419.00 
10790.00 
18199.00 
18499.00 

9601.00 
19772.00 

9203.00 
11004.00 
13252.00 
13253.00 
13990.00 
15583.00 
18896.00 
19154.00 



SKEETER BEATER INSECT REPELLENT 

AIR GUARD INSECT REPELLENT BUSH STRENGTH 

AMWAY D-15 INSECT REPELLENT 

AMWAY D-15 INSECT REPELLENT TOWELETTE 

UNCLE KEITH'S BUG FREE INSECT REPELLENT 

UNCLE KEITH'S BUG FREE JACKET 

DEET- 100 INSECT REPELLENT 

EN -GARDE LONG LASTING INSECT REPELLENT 

BRENTDALE CHEMICALS INSECT REPELLENT 

COMBAT INSECT REPELLENT 

COMBAT LIQUID INSECT REPELLENT 

CONN CHEM INSECT REPELLENT 

CCL QUICK- BREAKING INSECT REPELLENT FOAM II 

TANTOO REPELLENT 

TANTOO GEL 

COGHLANS INSECT REPELLENT 

COPELAND INSECT REPELLENT PRESSURIZED SPRAY 

DECA INSECT REPELLENT 

THE ORIGINAL SKEETO-BAN JACKET OR PANTS 

THE ORIGINAL SKEETO-BAN INSECT REPELLENT 

BUG STOP 100 

FULLER REPEL- GEL 

GOTCHA! INSECT REPELLENT 

RIVER TRAIL LIQUID INSECT REPELLENT 

CO-OP INSECT REPELLENT 

CO-OP INSECT REPELLENT PRESSURIZED SPRAY 

OFF! FRESH OUTDOOR SCENT INSECT REPELLENT 

OFF! INSECT REPELLENT 

DEEP WOODS FORMULA OFF INSECT REPELLENT LOTION 

DEEP WOODS PRESSURIZED SPRAY INSECT REPELLENT 

INSECT REPELLENT TOWELETTES 

PUMP SPRAY INSECT REPELLENT 
DEEP WOODS OFF! PUMP LIQUID 
DEEP WOODS MAXIMUM STRENGTH SPRAY 



OFF! 
OFF! 



196 



JOH 


21255. 


00 


J OH 


21299. 


00 


JOL 


19457. 


00 


JOL 


20710. 


00 


KSL 


18958. 


00 


KSL 


18959. 


00 


LAL 


18421. 


00 


MEI 


16486. 


00 


MLS 


18364. 


00 


MLS 


18365. 


00 


MLS 


18366. 


00 


MLS 


18367. 


00 


MLS 


19322. 


00 


NAC 


11140, 


00 


NOZ 


12401, 


00 


NOZ 


12402. 


00 


PGH 


18093, 


00 


PGH 


18778, 


00 


PGH 


19909, 


00 


PGH 


20455, 


00 


PIC 


14674, 


00 


PIC 


18105 


,00 


PIC 


18543, 


,00 


PUG 


17435 


,00 


RAW 


14153 


,00 


REC 


7137 


.00 


REC 


11219 


.00 


REC 


11430 


.00 


REC 


15351 


.00 


SAF 


16056 


.00 


SAF 


17341 


.00 


SAF 


18153 


.00 


SAF 


18707 


.00 


SAF 


19607 


.00 


SAN 


11309 


.00 


SEM 


18399 


.01 


SIH 


19910 


.00 


STL 


14292 


.00 


STL 


14293 


.00 


STL 


14294 


.00 


STO 


14316 


.00 


STO 


20489 


.00 


STT 


16970 


.00 


TET 


18326 


.00 


TNR 


20375 


.00 


TNR 


20376 


.00 



OFF! PRESSURIZED INSECT REPELLENT 

OFF! SKINTASTIC LOTION INSECT REPELLENT (WITH 

ALOE VERA) 

BITE FREE INSECT REPELLENT 

SUREKILLER BITE FREE II INSECT REPELLENT 

KELSEY TRAIL BUG BUSTER INSECT REPELLENT JACKET 

KELSEY TRAIL BUG BUSTER INSECT REPELLENT 

PROTECTION INSECT REPELLENT 

STOP BITE INSECT REPELLENT LIQUID 

CUTTER EVERGREEN SCENT INSECT REPELLENT 

CUTTER INSECT REPELLENT 

CUTTER EVERGREEN SCENT INSECT REPELLENT CREAM 

CUTTER INSECT REPELLENT CREAM 

CUTTER MAXIMUM STRENGTH INSECT REPELLENT LIQUID 

SWAT SPRAY INSECT REPELLENT 

NOXEMA INSECT REPELLENT LOTION 

NOXEMA TAN & GUARD LOTION 

THE ORIGINAL MUSKOL INSECT REPELLENT 

MUSKOL INSECT REPELLENT WITH SUNSCREEN 

MUSKOL INSECT REPELLENT SPRAY PRESSURIZED 

MUSKOL LITE INSECT REPELLENT SPRAY 

PIC INSECT REPELLENT LOTION 

PIC 75 DEET INSECT REPELLENT 

PIC X-100 DEET 

PARAS ECT INSECT REPELLENT 

RAWLEIGH INSECT REPELLENT 

NERO INSECT REPELLENT SOLUTION 

"Z" INSECT REPELLENT SOLUTION 

CANADIAN TIRE INSECT REPELLENT 

RECORD 100 INSECT REPELLENT 

SANEX JUNGLE POWER INSECT REPELLENT 

JUNGLE POWER INSECT REPELLENT 

JUNGLE POWER FOAM INSECT REPELLENT 

SANEX JUNGLE POWER PRESSURIZED SPRAY INSECT 

REPELLENT 

VET-TEK MUSTANG INSECT REPELLENT 

SANFAX BUG OFF INSECT REPELLENT 

HURK III INSECT REPELLENT 

BUZAWAY INSECT REPELLENT SPRAY 

6-12 PLUS INSECT REPELLENT STICK 

6-12 PLUS INSECT REPELLENT SPRAY 

6-12 PLUS INSECT REPELLENT LOTION 

REPEX INSECT REPELLENT 

REPEX INSECT REPELLENT PRESSURIZED SPRAY 

LIQUID INSECT REPELLENT NO 955 

BLAST INSECT REPELLENT 

BEN'S 100 SPRAY INSECT REPELLENT 

BEN'S 100 LOTION INSECT REPELLENT 



197 



TRO 


11841 


.00 


TRO 


18398 


.00 


WAL 


14326 


.00 


WDG 


19412 


.00 


WES 


18310 


.00 


WHS 


18399 


.02 


WIC 


20018 


.00 


WIC 


20392 


.00 


WIS 


17238 


.00 


WIS 


17239 


.00 


WIS 


18148 


.00 


WIS 


18194 


.00 


WIS 


18195 


.00 


ZOD 


16861 


.00 


ZOD 


20188 


.00 



TROJAN TRO -PELL TRL-455 

TROJAN CHEMICALS TRB-505 INSECT REPELLENT 

WATKINS INSECT REPELLENT LOTION 

WEDGCO BUZZ -OFF 

WILD ONE INSECT REPELLENT 

INSECT REPELLENT 

WIN INSECT REPELLENT II 

WIN PUMP INSECT REPELLENT IB 

REPEL 100 INSECT REPELLENT LIQUID 

REPEL INSECT REPELLENT LOTION 

REPEL INSECT REPELLENT PRESSURIZED SPRAY 

REPEL INSECT REPELLENT PUMP SPRAY 

REPEL 100 INSECT REPELLENT NON-AEROSOL PUMP 

ZOECON VAPORETTE REPEL 30 REPELLENT 

STARBAR EQUINE SUPER WIPE 



ETHYLHEXANEDIOL 



ALT 


9868 


.00 


ILD 


15835, 


.00 


JBL 


15433 


.00 


MRA 


19959 


.00 


MRA 


20779 


.00 


STL 


14292 


.00 


STL 


14293 


.00 


STL 


14294 


.00 


ZOC 


15008 


.00 



CHASSE INSECTES INSECT REPELLENT 

INLAND -ALCARE ELLIS INSECT REPELLENT 

BF-100 BLACK FLY REPELLENT 

X-IT INSECT REPELLENT 

X-IT INSECT REPELLENT STICK 

6-12 PLUS INSECT REPELLENT STICK 

6-12 PLUS INSECT REPELLENT SPRAY 

6-12 PLUS INSECT REPELLENT LOTION 

VAPORETTE REPEL PERSONAL INSECT REPELLENT 



OIL OF LAVENDER 

PEV 9930.00 FLY SCREEN 

BISBUTYLENE TETRAHYDROFURFURAL 



AIG 


14333 


.00 


AVM 


18312 


.00 


BAX 


10862 


.00 


BAX 


19659 


.00 


BDC 


18399 


.00 


BDC 


20837 


,00 


BOY 


17956 


.00 


CCN 


20498 


.00 


CCN 


20774 


.00 


CCN 


20817 


.00 


CGC 


4039 


.00 


CGC 


8679 


.00 


CGC 


12958 


.00 


COS 


18400 


.00 



AIR GUARD INSECT REPELLENT BUSH STRENGTH 

ATTACK INSECT REPELLENT 

PARA-S BOMB 

SPRAY N' REPEL 

BRENTDALE CHEMICALS INSECT REPELLENT 

INSECT REPELLENT 

COMBAT INSECT REPELLENT 

CCL INSECT REPELLENT III 

CCL QUICK- BREAKING INSECT REPELLENT FOAM II 

CCL PUMP INSECTICIDE SPRAY VII 

TANTOO REPELLENT 

TANTOO LIQ INSECT REPELLENT 

TANTOO GEL 

COPELAND INSECT REPELLENT PRESSURIZED SPRAY 



198 



FAR 


13923, 


00 


FFL 


19522. 


00 


FUB 


10790. 


00 


GUC 


18199. 


.00 


HAU 


15576. 


00 


HAU 


15577, 


00 


INT 


9601. 


,00 


INT 


19772. 


,00 


JAN 


18389 


,00 


JOH 


13252, 


,00 


JOH 


13253 


,00 


JOH 


19730 


.00 


JOH 


21299 


,00 


JOL 


19457 


.00 


JOL 


20710 


,00 


NAC 


11140 


,00 


PIC 


14674 


.00 


SAF 


18153 


.00 


SAF 


19607 


.00 


SAN 


11309 


.00 


SEM 


18399 


.01 


STO 


18041 


.00 


TRO 


18398 


.00 


WDG 


19412 


.00 


WES 


18310 


.00 


WHS 


18399 


.02 


WIC 


20018 


.00 


WIC 


20392 


.00 


ZOD 


20188 


.00 



SUPER SWAT FLY REPELLENT 

BUG STOP 50 

FULLER REPEL- GEL 

GOTCHA! INSECT REPELLENT 

HARTZ DOG FLEA & TICK SPRAY 

HARTZ CAT FLEA & TICK SPRAY 

CO-OP INSECT REPELLENT 

CO-OP INSECT REPELLENT PRESSURIZED SPRAY 

SIPHEX 14 INSECTICIDE WITH REPELLENT (FOR CATS 

& DOGS) 

DEEP WOODS FORMULA OFF INSECT REPELLENT LOTION 

DEEP WOODS PRESSURIZED SPRAY INSECT REPELLENT 

DEEP WOODS PUMP SPRAY INSECT REPELLENT 

OFF! SKINTASTIC LOTION INSECT REPELLENT (WITH 

ALOE VERA) 

BITE FREE INSECT REPELLENT 

SUREKILLER BITE FREE II INSECT REPELLENT 

SWAT SPRAY INSECT REPELLENT 

PIC INSECT REPELLENT LOTION 

JUNGLE POWER FOAM INSECT REPELLENT 

VET-TEK MUSTANG INSECT REPELLENT 

SANFAX BUG OFF INSECT REPELLENT 

HURK III INSECT REPELLENT 

REPEX INSECT REPELLENT 

TROJAN CHEMICALS TRB-505 INSECT REPELLENT 

WEDGCO BUZZ -OFF 

WILD ONE INSECT REPELLENT 

INSECT REPELLENT 

WIN INSECT REPELLENT II 

WIN PUMP INSECT REPELLENT IB 

STARBAR EQUINE SUPER WIPE 



DI-N- PROPYL ISOCINCHOMERONATE 



AFL 


16041 


.01 


AIG 


14333 


.00 


AVM 


18312 


.00 


BDC 


18399 


,00 


BDC 


20837 


.00 


BOY 


17956 


.00 


CCN 


20498 


.00 


CGC 


4039 


.00 


CGC 


12120 


.00 


CGC 


12958 


.00 


CLB 


20534 


.00 


COS 


18400 


.00 


EMO 


18587 


.00 


EMO 


18588 


.00 



DELLA DAIRY SPRAY 

AIR GUARD INSECT REPELLENT BUSH STRENGTH 

ATTACK INSECT REPELLENT 

BRENTDALE CHEMICALS INSECT REPELLENT 

INSECT REPELLENT 

COMBAT INSECT REPELLENT 

CCL INSECT REPELLENT III 

TANTOO REPELLENT 

CIBA-GEIGY PREMIUM LIVESTOCK SPRAY LIQUID 

TANTOO GEL 

PURGE FOAM INSECT REPELLENT FOR HORSES 

COPELAND INSECT REPELLENT PRESSURIZED SPRAY 

BANISH 

SWAT 



199 



EMO 


18589. 


00 


EMO 


18590. 


00 


FAR 


10375. 


00 


FAR 


13438. 


00 


FAR 


13554. 


00 


FAR 


13922. 


00 


FFL 


19522. 


00 


FUB 


10790, 


00 


GUC 


18199. 


00 


INT 


9601. 


,00 


INT 


19735. 


,00 


INT 


19772 


.00 


J OH 


13253 


,00 


JOL 


19457 


00 


JOL 


20710 


,00 


KEK 


18583 


,00 


KEK 


18584 


,00 


LOR 


12585 


.00 


MLS 


18365 


.00 


MLS 


18366 


,00 


MLS 


18367 


.00 


NAC 


11140 


.00 


PGH 


18093 


.00 


PGH 


18778 


.00 


PGH 


19909 


.00 


PGH 


20455 


.00 


PIC 


14674 


.00 


RAL 


10434 


,00 


SAF 


18153 


.00 


SAF 


18707 


.00 


SAF 


19607 


.00 


SAN 


11309 


.00 


SEM 


18399 


.01 


STO 


18041 


.00 


TRO 


18398 


.00 


WDG 


19412 


.00 


WES 


18310 


.00 


WHS 


18399 


.02 


WIC 


20392 


.00 


ZOD 


16041 


.00 


ZOD 


20188 


.00 



HOG -WASH 

EVICT 

FARNAM WIPE LIQ WIPE -ON FLY REPELLENT 

ROLL- ON FLY REPELLENT & INSECTICIDE 

FARNAM FLYS-AWAY REPELLENT BOMB II 

SWAT FLY REPELLENT CREAM 

BUG STOP 50 

FULLER REPEL- GEL 

GOTCHA! INSECT REPELLENT 

CO-OP INSECT REPELLENT 

CO-OP HORSE GARD INSECTICIDE REPELLENT 

CO-OP INSECT REPELLENT PRESSURIZED SPRAY 

DEEP WOODS PRESSURIZED SPRAY INSECT REPELLENT 

BITE FREE INSECT REPELLENT 

SUREKILLER BITE FREE II INSECT REPELLENT 

BODY GARD 

HORSE -SHOO 

LORRAIN RUB-ON LIQUID HORSE INSECTICIDE 

CUTTER INSECT REPELLENT 

CUTTER EVERGREEN SCENT INSECT REPELLENT CREAM 

CUTTER INSECT REPELLENT CREAM 

SWAT SPRAY INSECT REPELLENT 

THE ORIGINAL MUSKOL INSECT REPELLENT 

MUSKOL INSECT REPELLENT WITH SUNSCREEN 

MUSKOL INSECT REPELLENT SPRAY PRESSURIZED 

MUSKOL LITE INSECT REPELLENT SPRAY 

PIC INSECT REPELLENT LOTION 

PURINA RUB-ON EMULSION HORSE INSECTICIDE 

JUNGLE POWER FOAM INSECT REPELLENT 

SANEX JUNGLE POWER PRESSURIZED SPRAY INSECT 

VET-TEK MUSTANG INSECT REPELLENT 

SANFAX BUG OFF INSECT REPELLENT 

HURK III INSECT REPELLENT 

REPEX INSECT REPELLENT 

TROJAN CHEMICALS TRB-505 INSECT REPELLENT 

WEDGCO BUZZ -OFF 

WILD ONE INSECT REPELLENT 

INSECT REPELLENT 

WIN PUMP INSECT REPELLENT IB 

STARBAR DAIRY SPRAY WITH REPELLENT 

STARBAR EQUINE SUPER WIPE 



N-OCTYL BICYCLOHEPTENE DICARBOXIMIDE 

AIG 14333.00 AIR GUARD INSECT REPELLENT BUSH STRENGTH 
AVM 18312.00 ATTACK INSECT REPELLENT 
BAX 19659.00 SPRAY N' REPEL 



200 



BDC 


18399. 


00 


BOY 


17956. 


00 


CCN 


20774. 


00 


CCN 


20817. 


00 


CGC 


4039. 


00 


CGC 


8679. 


00 


CGC 


12958. 


00 


CLB 


20534. 


00 


COS 


18400. 


00 


EMO 


18587. 


00 


EMO 


18588. 


00 


EMO 


18589. 


00 


EMO 


18590. 


00 


FAR 


13438. 


00 


FAR 


13923. 


,00 


FFL 


19522, 


,00 


FUB 


10790. 


00 


GUC 


18199, 


,00 


HAU 


15576 


.00 


HAU 


15577, 


,00 


INT 


19735 


,00 


JAN 


18389 


.00 


JOH 


13252 


.00 


JOH 


19730 


.00 


JOL 


19457 


.00 


JOL 


20710 


.00 


KEK 


18583 


.00 


KEK 


18584 


.00 


LOR 


12585 


.00 


MLS 


18364 


.00 


MLS 


18366 


.00 


MLS 


18367 


.00 


NAC 


11140 


.00 


PGH 


18093 


.00 


PGH 


18778 


.00 


PGH 


20455 


.00 


PIC 


14674 


.00 


RAL 


10434 


.00 


SAF 


18707 


.00 


SAF 


19607 


.00 


SAN 


11309 


.00 


SEM 


18399 


.01 


STO 


18041 


.00 


TRO 


18398 


.00 


WDG 


19412 


.00 


WES 


18310 


.00 



BRENTDALE CHEMICALS INSECT REPELLENT 

COMBAT INSECT REPELLENT 

CCL QUICK- BREAKING INSECT REPELLENT FOAM II 

CCL PUMP INSECTICIDE SPRAY VII 

TANTOO REPELLENT 

TANTOO LIQUID INSECT REPELLENT 

TANTOO GEL 

PURGE FOAM INSECT REPELLENT FOR HORSES 

COPELAND INSECT REPELLENT PRESSURIZED SPRAY 

BANISH 

SWAT 

HOG -WASH 

EVICT 

ROLL-ON FLY REPELLENT & INSECTICIDE 

SUPER SWAT FLY REPELLENT 

BUG STOP 50 

FULLER REPEL- GEL 

GOTCHA! INSECT REPELLENT 

HARTZ DOG FLEA & TICK SPRAY 

HARTZ CAT FLEA & TICK SPRAY 

CO-OP HORSE GARD INSECTICIDE REPELLENT 

SIPHEX 14 INSECTICIDE WITH REPELLENT (FOR CATS 

& DOGS) 

DEEP WOODS FORMULA OFF INSECT REPELLENT LOTION 

DEEP WOODS PUMP SPRAY INSECT REPELLENT 

BITE FREE INSECT REPELLENT 

SUREKILLER BITE FREE II INSECT REPELLENT 

BODY GARD 

HORSE- SHOO 

LORRAIN RUB-ON LIQUID HORSE INSECTICIDE 

CUTTER EVERGREEN SCENT INSECT REPELLENT 

CUTTER EVERGREEN SCENT INSECT REPELLENT CREAM 

CUTTER INSECT REPELLENT CREAM 

SWAT SPRAY INSECT REPELLENT 

THE ORIGINAL MUSKOL INSECT REPELLENT 

MUSKOL INSECT REPELLENT WITH SUNSCREEN 

MUSKOL LITE INSECT REPELLENT SPRAY 

PIC INSECT REPELLENT LOTION 

PURINA RUB-ON EMULSION HORSE INSECTICIDE 

SANEX JUNGLE POWER PRESSURIZED SPRAY INSECT 

REPELLENT 

VET-TEK MUSTANG INSECT REPELLENT 

SANFAX BUG OFF INSECT REPELLENT 

HURK III INSECT REPELLENT 

REPEX INSECT REPELLENT 

TROJAN CHEMICALS TRB-505 INSECT REPELLENT 

WEDGCO BUZZ -OFF 

WILD ONE INSECT REPELLENT 



201 



WIC 20392.00 WIN PUMP INSECT REPELLENT IB 
ZOD 20188.00 STARBAR EQUINE SUPER WIPE 

APPENDIX II 

SPRAY EQUIPMENT USED IN CANADA FOR MOSQUITO CONTROL 

A wide variety of insecticide application equipment is used 
in mosquito control programs in Canada. Sprayers can be 
conveniently divided into equipment used for mosquito larviciding 
and for mosquito adulticiding. Some equipment may be used for 
either method of mosquito control (e.g., back-pack sprayers); 
other equipment may be used only for adulticiding (e.g. , ULV 
generators) . 

Although specific examples of spray equipment are given below 
to illustrate the choices available, mention of a particular 
product does not constitute endorsement. Other products, 
equivalent to those mentioned, may be available locally and 
perform equally well. 

Because most of the spray equipment used in Canada is 
manufactured in the U.S.A., tank sizes are given in U.S. gallons. 

Mosquito Larviciding 

(1) Portable, Manual 

(a) Hand-carried, liquid sprayer 

The standard, two- or three -gallon, pressurized- type , sprayer 
is often used to apply a larvicide to small-sized mosquito 
breeding sites. These simple sprayers (equipped with a stainless 
steel tank, an 8 -inch gun valve unit and wand, 4 feet of hose, and 
an adjustable nozzle tip assembly) can provide many years of 
service. An example is the B & G Extenda-Ban Model N-224S. 

(b) Neck-carried, granular applicator 

Sometimes referred to as "belly grinders", these units are 
bucket -shaped, have a rotary hand- crank for auguring granules 
through a bottom-mounted granule spreader, and are hung from the 
operator's neck. 

Most such spreaders are used to apply fertilizer or herbicide 
granules to home grounds . Although not used commonly for mosquito 
larviciding (because of the discomfort of the unit, the weight of 
granules, and its dust-generating properties), they can be useful 
when better granular application equipment is unavailable. A 
variety of makes and models are available at garden supply 
centres. 

(c) Back-Pack, liquid sprayer 

202 



Many brands of these multi-purpose sprayers are available. 
They are used to apply fertilizers, pesticides, spray water onto 
small fires, etc. Typically, a plastic, 20 L, tank is mounted to 
a back-pack harness and a side -mounted hand-pump lever is used to 
pressurize the tank, moving the insecticide through a 3 or 4 foot 
hose and the gun valve unit and wand. For larviciding, a coarse, 
pin-stream nozzle is most often used. An example is the CP3 Mk2 . 

(2) Portable, Powered 

(a) Back- Pack, liquid sprayer 

These units are powered by a small, gasoline engine. The 
tank is moulded above the engine and both are mounted to a back- 
pack carrier. Some units only dispense liquid sprays; others, 
depending on options, can dispense sprays as a mist and/or 
dispense granules. Although some units are very noisy and heavy, 
they are an efficient, low-cost means of spraying. An example of 
this type of sprayer is the Echo SHR-200E. 

A multi-mode example is the Echo Model DM-9. This versatile 
unit is a combination sprayer and duster. It can dispense a 
liquid spray, mist, dust or granules depending on the 
configuration of options used. In mosquito control work, it is 
used most often as either a mist-blower or as a granular appli- 
cator. 

(b) Back-pack, mist-blower 

These units are equipped with a special misting nozzle. 
These units can mist up to 10 m from the blower. See also 
discussion in 2 (a) above. An example is the Echo Model DM-9, 
described above. 

(c) Back-pack, granular applicator: 

The unit is equipped with a granule spreading nozzle. 
Granules can be spread up to 8-10 m from the unit, depending on 
nozzle angle and winds. See also discussion in 2 (a) above. 
An example is the Echo Model DM-9, described above. 

(3) Truck-mounted, powered 

(a) Liquid, hose and nozzle sprayer 

Because these types of sprayers are commonly used by 
commercial applicators and farmers to apply pesticides and 
fertilizers, there are countless makes and models available. 

One example is the Agrotec which, like many other such skid- 
mounted units, comes with a 100, 150, or 200 gallon tank and a 
gun, hose and reel kit. 

(b) Liquid, mist-blower 

203 



Mist-blowers used for tree spraying also can be used to apply 
a residual spray to mosquito resting and oviposition sites. A 
popular unit amongst mosquito abatement workers is the heavy- 
duty, mister-duster combination sprayer. These units have a 
liquid tank (or a 45 -gallon drum) and a granule hopper. Thus, 
they can be used to apply liquid mists or granules. One such unit 
is the Buffalo Turbine Sprayer-Duster Model K. 

(c) Granular -blower applicator. See (3)(c) above. 

(4) Trailer-mounted, powered: 

(a) Liquid, mist-blower 

These sprayers are typically used for spraying large trees to 
control defoliating insects but are also used by some 
municipalities to apply residual sprays to wide, roadside ditches 
to kill resting, adult mosquitoes. They are not suitable for 
small areas or narrow ditches. An example is the John Bean mist- 
blower or tree sprayer. Several models are used. 

(5) Aircraft -mounted, powered 

(a) Boom and nozzle sprayer 

Boom and nozzle liquid sprayers are not used commonly for 
mosquito larviciding because of problems associated with spray 
evaporation, drift and foliage penetration and difficult terrain. 
However, they are sometimes used to apply 'liquid larvicides to 
wide, drainage ditches, sewage lagoons and sloughs, using 
aircraft. 

Most equipment used on agricultural fixed- and rotary-wing 
aircraft is suitable. A commonly used brand is Simplex gear. 

(b) Granular applicator 

Granular larvicides are frequently applied by aircraft 
(mostly rotary-wing) to mosquito larval breeding sites. 

Simplex gear is probably the most often equipment used in 
Canada . 

Mosquito Adulticiding 

(1) Portable, Powered 

(a) Hand-carried, liquid sprayer 

Small, hand- carried, pressurized are not widely used for 
adult mosquito control. Their use is limited to applying a 
residual spray to walls of buildings (e.g., stables, homes), near 
doors and windows, where adult mosquitoes may rest or attempt to 
enter a structure. An example is the B & G Extenda-Ban Model N- 

204 



224S. 

(b) Hand- carried, thermal fogger 

These foggers thermal -pneumatically produce aerosol droplets 
10-60 microns in diameter. Most units have a 5-7 L tank for the 
fogging solution (usually a mixture of diesel and insecticide 
concentrate) . This type of aerosol generator uses relatively old 
technology and most mosquito abatement agencies have or are 
switching over to non-thermal aerosol generators (see below). 
Portable, propane, thermal foggers generally are not suitable for 
mosquito control. An example is the Swingfog Model SN 50. 

(c) Hand- carried, ULV generator 

Several light-weight, gasoline -powered units are available 
and suitable for smaller outdoor mosquito adulticiding. They have 
a limited tank capacity (usually 0.25-0.5 gallons). These units 
are popular for use around farms , golf courses , small parks and 
campgrounds. Care should be taken to select a unit that will 
stand up to normal use. The most commonly used unit in Canada is 
the Leco ULV P-l. 

(d) Back-Pack, liquid sprayer 

These units, equipped with a flat -fan nozzle, may be used to 
apply a residual spray around buildings and vegetation to kill 
resting mosquitoes. An example of the liquid only sprayer is the 
Echo SHR-200E. 

(e) Back-pack, mist-blower 

These units are much more efficient than the liquid sprayers 
above. They can treat larger mosquito resting sites must faster 
because of their greater swath width and powered, pumping system. 
An example is the Echo Model DM-9. 

(2) Truck- mounted, powered 

(a) Liquid, hose and nozzle sprayer 

As noted above, these types of sprayers are commonly used by 
commercial applicators and farmers to apply pesticides and 
fertilizers. As a result, there are countless makes and models 
available. Gasoline- or electric-powered units can be purchased 
or assembled locally from readily available components. 

One example is the Agrotec which, like many other such skid- 
mounted units, comes with a 100, 150, or 200 gallon tank and a 
gun, hose and reel kit. 

(b) Liquid, mist-blower 

Most such units have been developed for urban forestry and 
orchard use. Municipalities responsible for both mosquito and 

205 



tree pest management use these sprayers for both purposes. The 
heavy-duty units can apply a wide swath of mist of residual 
mosquito adulticide through mosquito resting and oviposition sites 
(e.g., wide, grassy, roadside ditches). An example of this type 
of mist-blower is the Buffalo Turbine Sprayer -Duster Model K. 

(c) Thermal fogger 

Based on the same principle as the hand- carried thermal 
foggers, these units thermally produce aerosol droplets 5-200 
microns in diameter. Heavy-duty, skid-mounted, models are usually 
used in routine mosquito fogging programs. As noted above, most 
mosquito abatement agencies have replaced their old thermal 
foggers with the more modern cold aerosol equipment. An example 
is the TIFA Model 100-E. 

(d) ULV generator 

Many different kinds of light-, medium- and heavy-duty ULV 
generators are available for skid- or fixed-mounting on all- 
terrain vehicles, trucks and trailers. Commonly-used brands 
include those of Leco, Londonaire, Microgen and Curtis -Dyna. Most 
units draw the adulticide from the original, unpressurized 20 L 
insecticide container. One of the most commonly-used, heavy- 
duty, gasoline -powered, skid-mounted units for mosquito 
adulticiding is the Leco Model HD. 

A relatively-new, battery-operated ULV generator is the 
Whispermist (Models 10 and 20) . This type of cold fogger can be 
powered using a separate 12 volt battery or the truck battery. It 
is a light-weight, medium duty model which has the advantage of 
being very quiet running. 

(3) Aircraft -mounted, powered 

(a) Boom and nozzle sprayer 

Conventional boom and nozzle sprayers, like those used for 
agricultural applications, can also be used to apply residual 
sprays for adult mosquito control. Several models are available 
from Simplex. 

(b) ULV generator 

ULV nozzles can be substituted for convention teejet nozzles 
to enable ULV applications of mosquito adulticides. Various types 
of such rotary atomizers are available. They may be driven by 
wind, hydraulics or electricity. Beecomist Model 360 spray- 
heads have been used successfully on both rotary- and fixed-wing 
aircraft. 



206 



APPENDIX III 



SUPPLIERS OF REPELLENTS AND INSECTICIDES 
COMMONLY USED FOR MOSQUITO CONTROL IN CANADA 



ABE ABELL WACO LTD., 246 ATWELL DR., REXDALE, ON, M9W 5B4. 
416-675-1635 

ABT ABBOTT LABORATORIES, CAPD D-928, NORTH CHICAGO, IL, 60064, 
USA. 
312-937-8904 

AFL ALFA - LAVAL AGRI, 2020 FISHER DR., PETERBOROUGH, ON, K9J 
7B7. 
705-876-3122 

AFY ALL FOR YOU PRODUCTS INC., BOX 179, SMEATON, SK, SO J 2 JO. 
306-426-2031 

AIG AIR GUARD CONTROL INC., 26 WATERMAN AVE., TORONTO, ON, M4B 
1Y5. 
416-499-8500 

ALT ALSI CIE LTEE, 150 RUE SEIGNEURIALE, C.P. 5040, BEAUPORT , 
• PQ, G1E 4Y6. 
418-661-6703 

AMW AMWAY CORP., 7575 E. FULTON RD., ADA, MI, 49355, USA. 
616-676-5428 

ARE ARCTIC TRADING CO. INC., P.O. BOX 910, CHURCHILL, MB, ROB 
0E0. 
204-675-2164 

ARI AMERICAN REPELLENT INC., 1200 JAMES RD. , N. LITTLE ROCK, 
AR, 72118, USA. 
501-851-2337 

AVM AVMOR LTD., 433 RUE STE-HELENE, MONTREAL, PQ, H2Y 2L1 . 
514-849-4541 

BAX BAYVET DIV. CHEMAGRO LTD., 77 BELFIELD RD., ETOBICOKE, ON, 
M9W 1G6. 
416-248-0771 

BDC BRENTDALE CHEMICALS, 41 RACINE RD., REXDALE, ON, M9W 2Z6 . 

207 



BOY BOYLE-MIDWAY CANADA LTD., 2 WICKMAN RD., TORONTO, ON, M8Z 
5M5. 
416-255-9163 

CCN CCL INDUSTRIES, 26 WATERMAN AVE., TORONTO, ON, M4B 1Y5 . 
416-755-9271 

CGC CIBA-GEIGY CAN/AG DIV. , 6860 CENTURY AVE., MISSISSAUGA, 
ON, L5N 2W5. 
416-821-4420 

CHH CHEMAGRO LTD., 256 BRITANNIA RD.E., MISSISSAUGA, ON, L4Z 
1S6. 
416-890-0332 

CHP CHIPMAN INC., 400 JONES RD . , P.O. BOX 9910, STONEY CREEK, 
ON, L8G 3Z1. 
416-643-4123 

CHZ COGHLAN'S LTD., 121 IRENE ST., WINNIPEG, MB, R3T 4C7 . 
204-284-9550 

CLB CLINE BUCKNER INC., SUBSIDIARY WATERBURY INC. CO., P.O.BOX 
640, 100 

CALHOUN ST., INDEPENDENCE, LA, 70443, USA. 
504-878-6751 

COS COPELAND LABORATORIES LTD., 41 RACINE RD., REXDALE, ON, 
M9W 2Z6. 
416-743-4272 

CYC CYANAMID CANADA INC., 88 MCNABB ST., MARKHAM, ON, L3R 6E6 . 
416-470-3600 

DEV DECA INVESTMENTS, P.O. BOX 1, KIRKLAND LAKE, ON, P2N 3M6 . 
705-567-7844 

DFT DRAFT ENTERPRISES LTD., 912 STRATHCONA RD. , EAST SELKIRK, 
MB, ROE 0M0. 
204-738-2656 

DIS PRODUITS VETERINAIRES DISPAR, 675 ST- PIERRE SUD, JOLIETTE, 
PQ, J6E 
3Z1. 
514-759-0497 

DIT DITCHLING CORP. LTD., P.O. BOX 395, DON MILLS, ON, M3C 

208 



2S7. 
416-438-6807 

DOW DOW CHEMICAL OF CANADA LTD., P.O. BOX 1012, MODELAND RD., 
SARNIA, ON, 
N7T 7K7. 
519-339-5029 

DTC DRUG TRADING CO. LTD., 1960 EGLINTON AVE. E. , BOX 335, 
STATION "A", SCARBOROUGH, ON, M1K 5C1. 
416-288-1100 

DUP DUPHAR B.V., C.J. VAN HOUTENLAAN 36, WEESP, 1381 CP, THE 
NETHERLANDS 

EMO EMPIRE INTERNATIONAL, P.O. BOX 695, STREETSVILLE POSTAL 
STATION, MISSISSAUGA, ON, L5M 2C2 

FAR FARNAM COMPANIES, 301 WEST OSBORN RD., PHOENIX, AZ, 
85013-3928, USA. 
602-285-1660 

FFL FLORA & FAUNA LABS . INC . , 8500 PILLSBURY AVE. SO., 
MINNEAPOLIS, MN, 55420, USA. 
612-881-6908 

FUB FULLER BRUSH CO., 1115 GUELPH LINE, P.O. BOX 5019, 
BURLINGTON, ON, L7R 3Z8 . 
416-335-8000 

GAX GARDEX CHEMICALS LTD., 246 ATTWELL DR., REXDALE, ON, M9W 
5B4. 
416-6751638 

GRA GREENLEAF GARDEN SUPPLIES, 4612 DAWSON ST., P.O. BOX 
8233S, BURNABY, BC, V5C 5P8. 
604-299-9505 

GUC GUARDIAN CHEMICALS, P.O. BOX 3029, FORT SASKATCHEWAN, AB, 
T8L 2T1. 

HAU HARTZ CANADA INC., 1125 TALBOT ST., ST. THOMAS, ON, N5P 
3W7. 
519-631-7660 

HOH HOME HARDWARE STORES LTD., 34 HENRY ST. W. , ST. JACOBS, 
ON, NOB 2N0. 
519-664-2252 

209 



ILD INLAND ALCARE JANITOR SUPPLIES, 10916-119 ST., EDMONTON, 
AB, T5H 3P4. 
403-453-5800 

INT INTERPROVINCIAL CO-OP LTD., 945 MARION ST., ST. BONIFACE, 
MB, R2J 0K7. 
204-233-3461 

JAN JANSSEN PHARMACEUTICA, ANIMAL HEALTH DIV. , 1-6705 
MILLCREEK DR., MISSISSAUGA, ON, L5N 5R9 . 
416-567-2504 

JBL LJB LABORATORIES, 1001 E. CASS ST., ST. JOHNS, MI, 48879, 
USA. 
517-224-4784 

JOH JOHNSON (S.C.) & SON LTD., 1 WEBSTER ST., BOX 520, 
BRANTFORD, ON, N3T 5R1 . 
519-756-7900 

JOL JOHN LIM CO. (THE), 1285 ST. MARY'S AVE., MISSISSAUGA, ON, 
L5E 1M8. 
416-271-2711 

KEK KEM MANUFACTURING CAN. LTD., 6660 CAMPOBELLO RD., 
MISSISSAUGA, ON, L5N 2L9 . 
416-826-8240 

KEM KEMSAN INC., 462 TRAFALGAR RD.BOX 727, OAKVILLE, ON, L6J 
5C1. 
416-8452271 

KSL KELSEY SPORTSWEAR LTD., 563 NOTRE DAME AVE., WINNIPEG, MB, 
R3B 1S5. 
204-786-1503 

LAL LALCO SUPERCO LTD., C.P.280 STATION ROSEMOUNT, MONTREAL, 
PQ, H1X 3B8. 

LAT LATER CHEMICALS LTD., 12080 HORSESHOE WAY, RICHMOND, BC, 
V7A 4V5. 
604-271-4224 

LOR LORRAIN, LEO LABS ENGR. , 6151 IRWIN ST., LASALLE, PQ, H8N 
1A1. 
514-366-4805 



210 



MBY RHONE POULENC CANADA INC., 2000 ARGENTIA RD., PLAZA 3, 
SUITE 400, MISSISSAUGA, ON, L5N 1V9 . 
416-821-4450 

MCO MCKIRDY (J.G.M.) LTD., 19 LAKELAND POINT DR., KINGSTON, 
ON, K7M 4E8. 
613-389-5573 

MEI MEIER, IAAN, 31 EDILOU DR., TORONTO, ON, M8W 4B1 

MLS MILES LABORATORIES INC., HOUSEHOLD PRODUCTS DIV. , 7123 W. 
65TH ST., CHICAGO, IL, 60638, USA. 
312-458-6100 

MRA MARTIN OUTDOOR PRODUCTS, O.B. FASAN, 169 AURORA HTS DR, 
AURORA, ON, L4G 2X1. 
416-841-6760 

MFX MORFLEX CHEM. CO., 2110 HIGH POINT RD., GREENSBORO, NC , 
27403, USA. 
919-292-1781 

NAC NATIONAL CHEMSEARCH OF CAN., DIV. OF NCH CANADA INC., 245 
ORENDA RD., BRAMALEA, ON, L6T 1E7 . 
416-457-5220 

NEW NEWVILLE COMPANY INC., P.O. BOX 5637, STATION "A", 
CALGARY, AB, T2H 1Y1 

NOZ NOXELL (CANADA) CORP., 3333 UNITY DR., MISSISSAUGA, ON, 
L5L 3T3. 
416-828-2500 

PEI ROUSSEL BIO CORP., 170 BEAVERBROOK RD., LINCOLN PARK, N J , 
07035, USA. 
201-628-7200 

PEV PETRUNKA, MARY, 6-2643 EAST ARTHUR ST., THUNDER BAY, ON, 
P7E 5P5. 
807-622-4972 



PGH SCHOLL-PLOUGH CANADA INC., 6400 NORTHAM, MISSISSAUGA, ON, 
L4J 1J1. 
416-755-4141 

PIC PIC CORP., 23 S. ESSEX AVE., ORANGE, N J , 07050, USA. 

211 



201-678-7300 

PUG INSECTICIDES PUROGUARD LTEE, 264 RUE QUERBES , DORION, PQ, 
J7V 1J7. 
514-455-7402 

RAL RALSTON PURINA CANADA INC., 6151 RUE IRWIN, LASALLE, PQ, 
H8N 1A1. 
514-366-2040 

RAW RAWLEIGH, W.T. CO. CAN. LTD., 354 ISABEY, ST. LAURENT, PQ, 
H4T 1W1. 
514-342-4212 

REC RECOCHEM INC., 131 EAST DR., BRAMPTON, ON, L6T 1B5 . 
416-791-1788 

SAF SANEX CHEMICALS LTD., 2695 SLOUGH ST., MISSISSAUGA, ON, 
L4T 1G2. 
416-677-4890 

SAN SANFAX INDUSTRIES LTD., TRANS CANADA HWY. , 1650 SOUTH 
SERVICE RD., DORVAL, PQ, H9P 1H9 . 
514-683-7700 

SEM SEAL CHEMICAL CORP. CANADA LTD, BOX 103, WINNIPEG, MB, R3C 
2G1. 
204-694-2545 

SIH SI-PHARM LTD., 192 FORSYTH RD., NEWMARKET, ON, L3Y 7X9. 

STD STANCHEM, A BUSINESS UNIT OF C-I-L INC., ATTN: D. 
MACLEAN, 43 JUTLAND RD. , TORONTO, ON, M8Z 2G6 . 
416-259-8231 

STL STERLING DRUG LTD., YONGE ST. S., AURORA, ON, L4G 3H6 . 
416-773-1122 

STO STANLEYKEM INC., P.O. BOX 2099, CAMBRIDGE, ON, N3C 2V6 . 
519-658-9449 



STT STANALEX DEVELOPMENTS INC., 392 VODDEN ST.E., BRAMPTON, 
ON, L6V 2N3. 

TET TENTEL ENTERPRISES, P.O. BOX 156, BARRIE, ON, L4M 4T2. 
705-436-4941 



212 



TNR TENDER CORP., P.O. BOX 42, INDUSTRIAL PARK, LITTLETON, NH, 
03561, USA. 
603-444-5464 

TRO TROJAN CHEMICALS, DIV. OF VALLEY CAMP LTD., 41 RACINE RD . , 
REXDALE, ON, M9W 2Z6 . 
416-741-7372 

UAG UNITED AGRI PRODUCTS, PO BOX 22116, 439 SOVEREIGN RD., 
LONDON, ON, N6C 4N0 . 
519-659-9111 

UCC UNION CARBIDE CANADA LTD., P.O. BOX 700, 
POINTE-AUX-TREMBL, PQ, H1B 5K8 . 
514-645-5311 

WAL WATKINS INC., 30-5 SCURFIELD BLVD.,, WINNIPEG, MB, R3Y 
1G3. 
204-489-1295 

WDG WEDGCO CHEMICAL LTD., 623 HUNTS CRES . N.W. , CALGARY, AB, 
T2K 4J2. 
403-291-2441 

WES WESCLEAN NORTHERN SALES LTD., P.O. BOX 1367, HAY RIVER, 
NT, X1A 2L8. 

WHS WHEELS MAINTENANCE PRODUCTS LTD., 60 SIGNET DRIVE, WESTON, 
ON, M9L 2Y4. 
416-740-5885 

WIC WIN CHEMICALS & EQUIPMENT LTD., 1295 EGLINTON AVE E., UNIT 
#11, MISSISSAUGA, ON, L4W 3E6 . 
416-625-9672 

WIS WISCONSIN PHARMACAL CO., 2977 HIGHWAY 60, P.O. BOX 198, 
JACKSON, WI, 53037, USA. 
414-677-4121 

ZOC ZOECON INDUSTRIES, 12200 DENTON DRIVE, DALLAS, TX, 75234, 
USA. 
214-243-2321 

ZOD ZOECON CANADA INC., 3-12 STANLEY COURT, WHITBY, ON, LIN 
8P9. 
416-430-2511 



213 



ZOE ZOECON CORP., 975 CALIFORNIA AVE., PALO ALTO, CA, 94304 
USA. 
415-857-1130 



214 



APPENDIX IV 

ARBOVIRUS SURVEILLANCE PROGRAMS IN CANADA, 1980 3 
Arbovirus surveillance programs entail monitoring of adult 
populations of vector species and transmission rates (using 
sentinel flocks or mammals), virus isolations, and diagnosis of 
amplifying and dead-end host infections. 

Arbovirus surveillance programs are presently carried out 
annually in Manitoba and Saskatchewan [for western equine 
encephalitis (WEE)], Newfoundland [for eastern equine encephalitis 
(EEE)] and Ontario [for St. Louis encephalitis (SLE)]. No 
programs are carried out in Alberta, British Columbia, the 
Maritimes, Quebec, or the Territories. The lack of surveillance 
in these regions is partly a result of the lack of human 
encephalitis cases in recent years. Provincial governments are 
not convinced of the need for surveillance. In Quebec there is no 
one in the government who is responsible to take action, should an 
outbreak occur. 

Manitoba 

Arbovirus surveillance is coordinated by the Manitoba 
Arbovirus Surveillance Committee, which was formed in 1976 after 
the 1975 outbreak of WEE. A surveillance program is carried out 
annually to predict (and prevent) outbreaks of WEE in the human 
population. Virus identification and diagnostic services are 
available at provincial public health and veterinary laboratories. 

Saskatchewan 

An annual arbovirus surveillance program is part of a long- 
term study initiated over 20 years ago. The surveillance program 
is a joint venture between scientists at the federal Research 
Station and the University of Saskatchewan (Department of 
Veterinary Microbiology) , who have expertise and facilities to 
identify arboviruses. 

Ontario 

Surveillance for St. Louis encephalitis was initiated after 
outbreaks of the disease in 1975. A reduction in incidence of 
human cases of the disease since has resulted in reduced support 
for surveillance. A surveillance program is being carried out 
through the joint efforts of University of Guelph and the Essex 



3 Chance, M. M. 1982. The Canada Biting Fly Centre. A 
feasibility study of the proposed Canada Biting Fly Centre. 
Final Rpt. DSS file no. 05SU. 01837-8-0177 . Contract ser. no. ISU78 
00295. 243pp. 



215 



County Abatement district. Expertise on mosquito -borne 
arboviruses is also available at Queen's University. 

The National Arbovirus Reference Centre (University of 
Toronto) provides information expertise, reagents, and 
identification (diagnostic and confirmatory) services on a 
national basis. It surveys occurrence and activity of arboviruses 
across the country. The expertise of its personnel is highly 
regarded by virologists and other experts. The Centre is 
cooperating in arbovirus surveillance programs in Ontario and 
Newfoundland . 

Other Regions 

The Animal Diseases Research Institute (Agriculture Canada, 
Ottawa) provides identification (confirmation) services of 
arbovirus infections of livestock. 

Expert virologists with facilities for identifying 
arboviruses are located in Vancouver (U.B.C.), Edmonton, 
(University of Alberta, Public Health Laboratory) and Montreal 
(Institute Armand- Frapp ier at l'Universite de Montreal) and 
Halifax (Dalhousie University/Izaak Walton Killam Hospital) . In 
Newfoundland, work is carried out in cooperation with the National 
Arbovirus Reference Centre. Personnel at U.B.C. , University of 
Saskatchewan, and Dalhousie have carried out surveys of 
arboviruses in the territories, Alberta, Ontario, Quebec and the 
Maritimes. 



216 



3 can-i-. 0C5 

3 1073 00077fll 2 fl